Oruka Therapeutics (ORKA) S-4/A 22 Jul 24 Registration of securities issued in business combination transactions (amended) Financial data

Document And Entity Information

Document And Entity Information	3 Months Ended
	Mar. 31, 2024
Document Information Line Items
Entity Registrant Name	ARCA BIOPHARMA, INC.
Document Type	S-4/A
Amendment Flag	true
Amendment Description	The issuances of (i) all shares of ARCA common stock in exchange for each share of Oruka common stock (including shares of Oruka common stock issued in the Oruka pre-closing financing), (ii) all shares of ARCA common stock issuable upon exercise of pre-funded warrants issued in exchange for pre-funded warrants to purchase shares of Oruka common stock sold in the Oruka pre-closing financing, and (iii) all shares of ARCA common stock issuable upon conversion of ARCA Series B Preferred Stock issued in exchange for each share of Oruka preferred stock, are intended to be covered by this registration statement on Form S-4 of which the accompanying proxy statement/prospectus is a part. There is no difference between the shares of ARCA common stock that will be issued in exchange for each share of Oruka common stock issued in the pre-closing financing, the shares of ARCA common stock that will be issued in exchange for each other share of Oruka common stock, the shares of ARCA common stock that will be issuable upon the exercise of pre-funded warrants that will be issued in exchange for pre-funded warrants to purchase shares of Oruka common stock sold in the pre-closing financing and the shares of ARCA common stock that will be issuable upon conversion of ARCA Series B Preferred Stock that will be issued in exchange for each share of Oruka preferred stock.
Entity Central Index Key	0000907654
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Incorporation, State or Country Code	DE

Balance Sheets (Unaudited)

Balance Sheets (Unaudited) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Current assets:
Cash and cash equivalents	$ 35,903	$ 37,431	$ 42,445
Other current assets	767	161	254
Total current assets	36,670	37,592	42,699
Right-of-use asset – operating	17	247	343
Property and equipment, net	7	10	25
Other assets	12	12	18
Total assets	36,706	37,861	43,085
Current liabilities:
Accounts payable	529	362	334
Accrued compensation and employee benefits	84	100	173
Accrued expenses and other liabilities	968	175	625
Total current liabilities	1,581	637	1,132
Operating lease liability, net of current portion		204	280
Total liabilities	1,581	841	1,412
Commitments and contingencies
Stockholders’ equity:
Preferred stock, $0.001 par value; 5 million shares authorized; no shares issued or outstanding at December 31, 2023 and 2022
Common stock, value	14	14	14
Additional paid-in capital	225,861	225,747	225,061
Accumulated deficit	(190,750)	(188,741)	(183,402)
Total stockholders’ equity	35,125	37,020	41,673
Total liabilities and stockholders’ equity	$ 36,706	$ 37,861	$ 43,085

Balance Sheets (Unaudited) (Par

Balance Sheets (Unaudited) (Parentheticals) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Accrued expenses and other liabilities - related party (in Dollars)	$ 968	$ 175	$ 625
Preferred stock, par value (in Dollars per share)		$ 0.001	$ 0.001
Preferred stock, shares authorized		5,000,000	5,000,000
Preferred stock, issued		0	0
Preferred stock, outstanding		0	0
Common stock, par value (in Dollars per share)	$ 0.001	$ 0.001	$ 0.001
Common stock, shares authorized	100,000,000	100,000,000	100,000,000
Common stock, shares issued	14,501,143	14,501,143	14,410,143
Common stock, shares outstanding	14,501,143	14,501,143	14,410,143
Related Party
Accrued expenses and other liabilities - related party (in Dollars)		$ 0	$ 216

Statements of Operations (Unaud

Statements of Operations (Unaudited) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023	Dec. 31, 2022
Costs and expenses:
General and administrative	$ 2,317	$ 1,406	$ 6,283	$ 5,847
Research and development	165	390	1,013	4,749
Total costs and expenses	2,482	1,796	7,296	10,596
Loss from operations	(2,482)	(1,796)	(7,296)	(10,596)
Interest and other income	473	450	1,957	675
Other loss				(5)
Net loss	$ (2,009)	$ (1,346)	$ (5,339)	$ (9,926)
Net loss per share:
Basic (in Dollars per share)	$ (0.14)	$ (0.09)	$ (0.37)	$ (0.69)
Weighted average shares outstanding:
Basic (in Shares)	14,501,143	14,410,143	14,415,877	14,410,143

Statements of Operations (Una_2

Statements of Operations (Unaudited) (Parentheticals) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023	Dec. 31, 2022
Diluted	$ (0.14)	$ (0.09)	$ (0.37)	$ (0.69)
Diluted	14,501,143	14,410,143	14,415,877	14,410,143
Related Party
Related party expense	$ 0	$ 108	$ (91)	$ 432

Statements of Stockholders_ Equ

Statements of Stockholders’ Equity (Unaudited) - USD ($) $ in Thousands	Common Stock	Additional Paid-In Capital	Accumulated Deficit	Total
Balance at Dec. 31, 2021	$ 14	$ 224,505	$ (173,476)	$ 51,043
Balance (in Shares) at Dec. 31, 2021	14,410,143
Share-based compensation		556		556
Net loss			(9,926)	(9,926)
Balance at Dec. 31, 2022	$ 14	225,061	(183,402)	$ 41,673
Balance (in Shares) at Dec. 31, 2022	14,410,143			14,410,143
Share-based compensation		204		$ 204
Net loss			(1,346)	(1,346)
Balance at Mar. 31, 2023	$ 14	225,265	(184,748)	40,531
Balance (in Shares) at Mar. 31, 2023	14,410,143
Balance at Dec. 31, 2022	$ 14	225,061	(183,402)	$ 41,673
Balance (in Shares) at Dec. 31, 2022	14,410,143			14,410,143
Issuance of common stock upon vesting of Restricted Stock Units
Issuance of common stock upon vesting of Restricted Stock Units (in Shares)	91,000
Share-based compensation		686		686
Net loss			(5,339)	(5,339)
Balance at Dec. 31, 2023	$ 14	225,747	(188,741)	$ 37,020
Balance (in Shares) at Dec. 31, 2023	14,501,143			14,501,143
Balance at Mar. 31, 2023	$ 14	225,265	(184,748)	$ 40,531
Balance (in Shares) at Mar. 31, 2023	14,410,143
Share-based compensation		187		187
Net loss			(1,480)	(1,480)
Balance at Jun. 30, 2023	$ 14	225,452	(186,228)	39,238
Balance (in Shares) at Jun. 30, 2023	14,410,143
Share-based compensation		154		154
Net loss			(1,424)	(1,424)
Balance at Sep. 30, 2023	$ 14	225,606	(187,652)	37,968
Balance (in Shares) at Sep. 30, 2023	14,410,143
Issuance of common stock upon vesting of Restricted Stock Units
Issuance of common stock upon vesting of Restricted Stock Units (in Shares)	91,000
Share-based compensation		141		141
Net loss			(1,089)	(1,089)
Balance at Dec. 31, 2023	$ 14	225,747	(188,741)	$ 37,020
Balance (in Shares) at Dec. 31, 2023	14,501,143			14,501,143
Share-based compensation		114		$ 114
Net loss			(2,009)	(2,009)
Balance at Mar. 31, 2024	$ 14	$ 225,861	$ (190,750)	$ 35,125
Balance (in Shares) at Mar. 31, 2024	14,501,143			14,501,143

Statements of Cash Flows (Unaud

Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023	Dec. 31, 2022
Cash flows from operating activities:
Net loss	$ (2,009)	$ (1,346)	$ (5,339)	$ (9,926)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	3	4	15	20
Amortization of right-of-use asset – operating	16	25	96	94
Share-based compensation	114	204	686	556
Loss from disposal of property and equipment				5
Change in operating assets and liabilities:
Other current assets	(606)	(598)	93	808
Other assets			6
Accounts payable	167	32	28	(783)
Accrued compensation and employee benefits	(16)	62	(73)	(752)
Accrued expenses and other liabilities	803	22	(526)	(934)
Net cash used in operating activities	(1,528)	(1,595)	(5,014)	(10,912)
Cash flows from investing activities:
Purchase of property and equipment				(2)
Net cash used in investing activities				(2)
Cash flows from financing activities:
Net cash provided by financing activities
Net decrease in cash and cash equivalents	(1,528)	(1,595)	(5,014)	(10,914)
Cash and cash equivalents, beginning of year	37,431	42,445	42,445	53,359
Cash and cash equivalents, end of year	35,903	40,850	37,431	42,445
Supplemental cash flow information:
Interest paid
Income tax refund received
Supplemental disclosure of noncash investing and financing transactions:
Leased assets and operating lease liabilities – amended lease term	$ 214

ARCA and Summary of Significant

ARCA and Summary of Significant Accounting Policies	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
ARCA and Summary of Significant Accounting Policies [Abstract]
ARCA and Summary of Significant Accounting Policies	(1) ARCA and Summary of Significant Accounting Policies Description of Business ARCA biopharma, Inc. (“ARCA”), a Delaware corporation, is headquartered in Westminster, Colorado. ARCA is dedicated to applying a precision medicine approach to the development and commercialization of genetically targeted therapies for cardiovascular diseases. ARCA’s lead product candidate is Gencaro™ (bucindolol hydrochloride) for the treatment of atrial fibrillation (“AF”) in patients with chronic heart failure (“HF”). In April 2022, ARCA established a Special Committee of the board of directors (the “Board”) of ARCA to conduct a comprehensive review of strategic alternatives. As part of the strategic review process, ARCA explored potential strategic alternatives that included, without limitation, an acquisition, merger, business combination or other transactions. ARCA has and is continuing to explore strategic alternatives related to its product candidates and related assets, including, without limitation, licensing transactions and asset sales. On April 3, 2024, following a comprehensive review of strategic alternatives, ARCA, Atlas Merger Sub Corp., a Delaware corporation and a wholly -owned -owned ” -free ARCA’s future operations are highly dependent on the success of the Merger and there can be no assurances that the Merger will be successfully consummated. In the event that ARCA does not complete the Merger, it may explore strategic alternatives, including, without limitation, another strategic transaction and/or pursue a dissolution and liquidation of ARCA. See Note 10. Liquidity and Going Concern ARCA devotes substantially all of its efforts towards obtaining regulatory approval and raising capital necessary to fund its operations and it is subject to a number of risks associated with clinical research and development, including dependence on key individuals, the development of and regulatory approval of commercially viable products, the need to raise adequate additional financing necessary to fund the development and commercialization of its products, and competition from larger companies. ARCA has not generated revenue to date and has incurred substantial losses and negative cash flows from operations since its inception. ARCA has historically funded its operations through issuances of common and preferred stock. ARCA believes that its current cash and cash equivalents as of March 31, 2024 will be sufficient to fund its operations through the middle of fiscal year 2025. The future viability of ARCA beyond that point is dependent on the results of the strategic review process and its ability to raise additional capital to fund its operations. ARCA expects to continue to incur costs and expenditures in connection with the process of evaluating strategic alternatives. There can be no assurance, however, that ARCA will be able to successfully consummate any particular strategic transaction, including the Merger Agreement. The process of continuing to evaluate these strategic options may be very costly, time -consuming able to execute any strategic transaction. Changing circumstances may cause ARCA to consume capital significantly faster or slower than currently anticipated. ARCA has based these estimates on assumptions that may prove to be wrong, and it could exhaust its available financial resources sooner than it currently anticipates. Depending on the results of the strategic review process, ARCA may have to raise additional capital for clinical trials of Gencaro and to fund its operations. ARCA may not be able to raise sufficient capital on acceptable terms, or at all, to continue development of Gencaro or rNAPc2 or to otherwise continue operations and may not be able to execute any strategic transaction. ARCA’s liquidity, and its ability to raise additional capital or complete any strategic transaction, depends on a number of factors, including, but not limited to, the following: • • • • • • • • • The sale of additional equity or convertible debt securities would likely result in substantial additional dilution to ARCA’s stockholders. If ARCA raises additional funds through the incurrence of indebtedness, the obligations related to such indebtedness would be senior to rights of holders of ARCA’s capital stock and could contain covenants that would restrict ARCA’s operations. ARCA also cannot predict what consideration might be available, if any, to it or its stockholders, in connection with any strategic transaction. Should strategic alternatives or additional capital not be available to ARCA, or not be available on acceptable terms, ARCA may be unable to realize value from its assets and discharge its liabilities in the normal course of business which may, among other alternatives, cause ARCA to further delay, substantially reduce or discontinue operational activities to conserve its cash resources. Basis of Presentation The accompanying unaudited financial statements of ARCA were prepared in accordance with generally accepted accounting principles for interim financial information and pursuant to Regulation S -X strategic alternatives for further developing and commercializing Gencaro and rNAPc2, and raising capital. These unaudited financial statements should be read in conjunction with the audited financial statements and footnotes thereto for the year ended December 31, 2023 included elsewhere in this proxy statement/prospectus. Amounts presented are rounded to the nearest thousand, where indicated, except per share data and par values. Concentrations of Credit Risk Financial instruments that potentially subject ARCA to significant concentrations of credit risk consist primarily of cash and cash equivalents. ARCA has no off -balance-sheet Comprehensive Loss Comprehensive loss is defined as the change in equity during a period from transactions and other events and/or circumstances from non -owner Leases ARCA determines if an arrangement is a lease at inception. Operating leases are included in right -of-use ROU lease assets represent ARCA’s right to use an underlying asset for the lease term and lease obligations represent ARCA’s obligation to make lease payments arising from the lease. Operating ROU lease assets are recognized at the commencement date based on the present value of lease payments over the lease term. As ARCA’s leases do not provide an implicit rate, ARCA uses its incremental borrowing rate based on the information available at the commencement date in determining the present value of lease payments. ARCA’s lease terms may include options to extend or terminate a lease when it is reasonably certain that ARCA will exercise that option. Lease expense for lease payments is recognized on a straight -line Accrued Outsourcing Expenses As part of the process of preparing its financial statements, ARCA is required to estimate accrued outsourcing expenses. This process involves identifying services that third parties have performed on ARCA’s behalf and estimating the level of service performed and the associated cost incurred for these services as of the balance sheet date. Examples of estimated accrued outsourcing expenses include contract service fees, such as fees payable to contract manufacturers in connection with the production of materials related to ARCA’s drug product, and service fees and pass through costs from clinical research organizations. ARCA develops estimates of liabilities using its judgment based upon the facts and circumstances known at the time. Recent Accounting Pronouncements ARCA reviewed recently issued accounting pronouncements and concluded that they were either not applicable or not expected to have a significant impact to the financial statements.	(1) ARCA and Summary of Significant Accounting Policies Description of Business ARCA biopharma, Inc. (“ARCA”), a Delaware corporation, is headquartered in Westminster, Colorado. ARCA is a clinical -stage In April 2022, the Board of Directors established a Special Committee and, in May 2022, retained Ladenburg Thalmann & Co. Inc. to evaluate strategic options, including transactions involving a merger, sale of all or part of ARCA’s assets, or other alternatives with the goal of maximizing stockholder value. ARCA does not have a defined timeline for the strategic review process and the review may not result in any specific action or transaction. Liquidity and Going Concern ARCA devotes substantially all of its efforts towards obtaining regulatory approval and raising capital necessary to fund its operations and it is subject to a number of risks associated with clinical research and development, including dependence on key individuals, the development of and regulatory approval of commercially viable products, the need to raise adequate additional financing necessary to fund the development and commercialization of its products, and competition from larger companies. ARCA has not generated revenue to date and has incurred substantial losses and negative cash flows from operations since its inception. ARCA has historically funded its operations through issuances of common and preferred stock. ARCA believes that its current cash and cash equivalents as of December 31, 2023 will be sufficient to fund its operations through the middle of fiscal year 2025. ARCA’s review of its strategic options may impact this projection. Changing circumstances may cause ARCA to consume capital significantly faster or slower than currently anticipated. ARCA has based these estimates on assumptions that may prove to be wrong, and ARCA could exhaust its available financial resources sooner than it currently anticipates. Therefore, ARCA will have to raise additional capital for clinical trials of Gencaro. ARCA may not be able to raise sufficient capital on acceptable terms, or at all, to continue development of Gencaro or rNAPc2 or to otherwise continue operations and may not be able to execute any strategic transaction. ARCA’s liquidity, and its ability to raise additional capital or complete any strategic transaction, depends on a number of factors, including, but not limited to, the following: • • • • • • • The sale of additional equity or convertible debt securities would likely result in substantial additional dilution to ARCA’s stockholders. If ARCA raises additional funds through the incurrence of indebtedness, the obligations related to such indebtedness would be senior to rights of holders of ARCA’s capital stock and could contain covenants that would restrict ARCA’s operations. ARCA also cannot predict what consideration might be available, if any, to it or its stockholders, in connection with any strategic transaction. Should strategic alternatives or additional capital not be available to ARCA, or not be available on acceptable terms, ARCA may be unable to realize value from its assets and discharge its liabilities in the normal course of business which may, among other alternatives, cause ARCA to further delay, substantially reduce or discontinue operational activities to conserve its cash resources. Basis of Presentation The accompanying financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“GAAP”) and include all adjustments necessary for the fair presentation of ARCA’s financial position, results of operations and cash flows for the periods presented. Management has performed an evaluation of ARCA’s activities through the date of filing of the Annual Report on Form 10 -K Recent Accounting Pronouncements ARCA reviewed all other recently issued accounting pronouncements and concluded that they were either not applicable or not expected to have a significant impact to the financial statements. Accounting Estimates in the Preparation of Financial Statements The preparation of financial statements in conformity with accounting principles generally accepted in the United States of America requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of expenses during the reporting period. ARCA bases estimates on various assumptions that are believed to be reasonable under the circumstances. ARCA believes significant judgment was involved in estimating the outsourcing expenses, and in estimating other accrued liabilities and income taxes. Management is continually evaluating and updating these estimates, and it is possible that these estimates will change in the future or that actual results may differ from these estimates. Cash Equivalents Cash equivalents generally consist of money market funds and debt securities with maturities of 90 days or less at the time of purchase. ARCA invests its excess cash in securities with strong ratings and has established guidelines relative to diversification and maturity with the objective of maintaining safety of principal and liquidity. Concentrations of Credit Risk Financial instruments that potentially subject ARCA to significant concentrations of credit risk consist primarily of cash and cash equivalents. ARCA has no off -balance-sheet Property and Equipment Property and equipment are stated at cost less accumulated depreciation and amortization. Cost includes expenditures for equipment, leasehold improvements, replacements, and renewals. Maintenance and repairs are charged to expense as incurred. When assets are sold, retired, or otherwise disposed of, the cost and accumulated depreciation are removed from the accounts and any resulting gain or loss is reflected in operations. The cost of property and equipment is depreciated using the straight -line Comprehensive Loss Comprehensive loss is defined as the change in equity during a period from transactions and other events and/or circumstances from non -owner Leases ARCA determines if an arrangement is a lease at inception. Operating leases are included in right -of-use ROU lease assets represent ARCA’s right to use an underlying asset for the lease term and lease obligations represent ARCA’s obligation to make lease payments arising from the lease. Operating ROU lease assets are recognized at the commencement date based on the present value of lease payments over the lease term. As ARCA’s lease does not provide an implicit rate, ARCA uses its incremental borrowing rate based on the information available at the commencement date in determining the present value of lease payments. ARCA’s lease terms may include options to extend or terminate the lease when it is reasonably certain that ARCA will exercise that option. Lease expense for lease payments is recognized on a straight -line Accrued Outsourcing Expenses As part of the process of preparing its financial statements, ARCA is required to estimate accrued outsourcing expenses. This process involves identifying services that third parties have performed on ARCA’s behalf and estimating the level of service performed and the associated cost incurred for these services as of the balance sheet date. Examples of estimated accrued outsourcing expenses include contract service fees, such as fees payable to contract manufacturers in connection with the production of materials related to ARCA’s drug product, and service fees and pass through costs from clinical research organizations. ARCA develops estimates of liabilities using its judgment based upon the facts and circumstances known at the time. Segments ARCA operates in one segment. Management uses one measure of profitability and does not segment its business for internal reporting. Research and Development Research and development costs are expensed as incurred. These consist primarily of salaries, contract services, and supplies. Costs, if any, related to clinical trial and drug manufacturing activities are based upon estimates of the services received and related expenses incurred by contract research organizations (“CROs”), clinical study sites, drug manufacturers, collaboration partners, laboratories, consultants, or otherwise. Related contracts vary significantly in length, and could be for a fixed amount, a variable amount based on actual costs incurred, capped at a certain limit, or for a combination of these elements. Activity levels are monitored through communications with the vendors, including detailed invoices and task completion review, analysis of expenses against budgeted amounts, and pre -approval an estimate of costs incurred but not invoiced on a periodic basis. Expenses related to the CROs and clinical studies, as well as contract drug manufacturers, are primarily based on progress made against specified milestones or targets in each period. In accordance with certain research and development agreements, ARCA is obligated to make certain upfront payments upon execution of the agreement. ARCA records these upfront payments as prepaid research and development expenses, which are included in Other current assets or Other assets in the accompanying Balance Sheets. Such payments are recorded to research and development expense as services are performed. ARCA evaluates on a quarterly basis whether events and circumstances have occurred that may indicate impairment of remaining prepaid research and development expenses. Stock-Based Compensation ARCA’s stock -based -based -line Income Taxes The current benefit for income taxes represents actual or estimated amounts payable or refundable on tax returns filed or to be filed each year. Deferred tax assets and liabilities are recognized for the estimated future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases and operating loss and tax credit carryforwards. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in the period that includes the enactment date. The overall change in deferred tax assets and liabilities for the period measures the deferred tax expense or benefit for the period. The measurement of deferred tax assets may be reduced by a valuation allowance based on judgmental assessment of available evidence if deemed more likely than not that some or all of the deferred tax assets will not be realized.

Net Loss Per Share

Net Loss Per Share	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Net Loss Per Share [Abstract]
Net Loss Per Share	(2) Net Loss Per Share ARCA calculates basic loss per share by dividing net loss by the weighted average common shares outstanding during the period. Diluted loss per share is computed by dividing net loss by the weighted average number of common shares outstanding during the period increased to include, if dilutive, the number of additional common shares that would have been outstanding if the potential common shares had been issued. ARCA’s potentially dilutive shares include stock options and restricted stock units. Because ARCA reported a net loss for the three months ended March 31, 2024 and 2023, all potentially dilutive shares of ARCA common stock have been excluded from the computation of the dilutive net loss per share for all periods presented. Such potentially dilutive shares of ARCA common stock consist of the following: March 31, 2024 2023 Potentially dilutive securities, excluded: Outstanding stock options 645,845 664,857 Unvested restricted stock units — 91,000 645,845 755,857	(2) Net Loss Per Share ARCA calculates basic loss per share by dividing net loss by the weighted average common shares outstanding during the period. Diluted loss per share is computed by dividing net loss by the weighted average number of common shares outstanding during the period increased to include, if dilutive, the number of additional common shares that would have been outstanding if the potential common shares had been issued. ARCA’s potentially dilutive shares include stock options and restricted stock units. Because ARCA reported a net loss for the years ended December 31, 2023 and 2022, all potentially dilutive shares of ARCA common stock have been excluded from the computation of the dilutive net loss per share for all periods presented. Such potentially dilutive shares of ARCA common stock consist of the following: Years Ended 2023 2022 Potentially dilutive securities, excluded: Outstanding stock options 616,707 704,960 Unvested restricted stock units — 91,000 616,707 795,960

Fair Value Disclosures

Fair Value Disclosures	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Fair Value Disclosures [Abstract]
Fair Value Disclosures	(3) Fair Value Disclosures There were no Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date (“exit price”). Inputs used to measure fair value are classified into the following hierarchy: • • • As of March 31, 2024 and December 31, 2023, ARCA had $35.9 million and $37.4 million, respectively, of cash equivalents consisting of money market funds with original maturities of 90 days or less. ARCA has the ability to liquidate these investments without restriction. ARCA determines fair value for these money market funds with Level 1 inputs through quoted market prices. There were no Fair Value of Other Financial Instruments The carrying amount of other financial instruments, including accounts payable, approximated fair value due to their short maturities.	(3) Fair Value Disclosures Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date (“exit price”). Inputs used to measure fair value are classified into the following hierarchy: • • • As of December 31, 2023 and 2022, ARCA had $37.4 million and $42.4 million, respectively, of cash equivalents consisting of money market funds with original maturities of 90 days or less. ARCA has the ability to liquidate these investments without restriction. ARCA determines fair value for these money market funds with Level 1 inputs through quoted market prices. There were no Fair Value of Other Financial Instruments The carrying amount of other financial instruments, including accounts payable, approximated fair value due to their short maturities. As of December 31, 2023 and 2022, ARCA did not

Property and Equipment

Property and Equipment	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Property and Equipment [Abstract]
Property and Equipment	(4) Property and Equipment Property and equipment consist of the following (in thousands): Estimated March 31, December 31, Computer equipment 3 years $ 39 $ 39 Lab equipment 5 years 130 130 Furniture and fixtures 5 years 37 37 Computer software 3 years 16 16 222 222 Accumulated depreciation and amortization (215 ) (212 ) Property and equipment, net $ 7 $ 10 For the three months ended March 31, 2024 and 2023, depreciation and amortization expense was $3,000 and $4,000 respectively.	(4) Property and Equipment Property and equipment consist of the following (in thousands): Estimated December 31, December 31, Computer equipment 3 years $ 39 $ 39 Lab equipment 5 years 130 130 Furniture and fixtures 5 years 37 44 Computer software 3 years 16 16 222 229 Accumulated depreciation and amortization (212 ) (204 ) Property and equipment, net $ 10 $ 25 For the years ended December 31, 2023 and 2022, depreciation and amortization expense was $15,000 and $20,000, respectively.

Related Party Arrangements

Related Party Arrangements	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Related Party Arrangements [Abstract]
Related Party Arrangements	(5) Related Party Arrangements Transactions with ARCA’s Former President and Chief Executive Officer ARCA has entered into unrestricted research grants with its former President and Chief Executive Officer’s academic research laboratory at the University of Colorado. Funding of any unrestricted research grants is contingent upon ARCA’s financial condition, and can be deferred or terminated at ARCA’s discretion. There was no expense under these arrangements for the three months ended March 31, 2024. Total expense under these arrangements for the three months ended March 31, 2023 was $108,000. In December 2023, ARCA made a payment of $125,000 for the grant period July 2022 through December 2023 under these arrangements. In April 2024, the President and Chief Executive Officer resigned, see Note 10.	(5) Related Party Arrangements Transactions with ARCA’s President and Chief Executive Officer ARCA has entered into unrestricted research grants with its President and Chief Executive Officer’s academic research laboratory at the University of Colorado. Funding of any unrestricted research grants is contingent upon ARCA’s financial condition, and can be deferred or terminated at ARCA’s discretion. Total expense under these arrangements for the years ended December 31, 2023 and 2022 was $(91,000) and $432,000, respectively. In December 2023, ARCA made a payment of $125,000 for the grant period July 2022 through December 2023 under these arrangements.

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	(6) Commitments and Contingencies ARCA has or is subject to the following commitments and contingencies. Employment Agreements and Reduction of Workforce ARCA maintains employment agreements with several key executive employees. The agreements may be terminated at any time by ARCA with or without cause upon written notice to the employee, and entitle the employee to wages in lieu of notice for periods not exceeding one calendar year from the date of termination without cause or by the employee for good reason. Certain of these agreements also provide for payments to be made under certain conditions related to a change in control of ARCA. In December 2022, ARCA’s Board of Directors approved retention bonuses for certain employees, subject to continued employment with ARCA through the earlier of a change in control of ARCA or certain clinical development decisions totaling $265,000. In November 2023, the retention bonuses were amended to increase the aggregate amount of the retention bonus by 50% and in order to assist with tax obligations associated with the vesting of certain Company restricted stock unit awards in December 2023, a total of $86,000 was paid in December 2023. As of March 31, 2024, the unpaid retention bonuses totaled $311,000, none of which was accrued as of March 31, 2024, since there had not been a change in control or clinical development decision. In April 2024, the retention bonuses were again amended to increase the aggregate amount of the retention bonus, with the unpaid retention bonus increasing to $444,000. See Note 10. ARCA and Christopher D. Ozeroff, the former Secretary, Senior Vice President and General Counsel of ARCA mutually agreed to conclude Mr. Ozeroff’s employment effective March 31, 2023. Pursuant to Mr. Ozeroff’s existing employment agreement, as previously amended, ARCA provided Mr. Ozeroff severance benefits pursuant to the terms of his existing employment agreement with ARCA, as previously amended. The severance benefits included severance payments and reimbursement to cover out -of-pocket none ARCA and Dr. Michael Bristow, former President, Chief Executive Officer and a member of the board of directors of ARCA mutually agreed to conclude Dr. Bristow’s employment and service as a director, effective April 3, 2024. See Note 10. Operating Leases On August 29, 2020 ARCA entered into a lease agreement for approximately 5,200 square feet of office facilities in Westminster, Colorado which serves as its primary business office effective October 1, 2020 (“October 2020 Lease”). The lease term was 42 months beginning October 1, 2020. In March 2024, ARCA entered into an amendment to extend the lease term six (6) months through September 2024. If ARCA elects to stay in the property after September 2024, it will pay rent month to month equal to 125% of the base rent paid in September 2024. In June 2021, ARCA entered into a sublease agreement for approximately 3,000 square feet of additional office facilities in its primary business office (“2021 Lease”). The sublease term was 29 months and terminated in October 2023. The leases include real estate taxes and insurance, which is not a lease component and is not included in the lease obligation. In addition, common area maintenance charges are based on actual costs incurred and are a non -lease Future minimum commitments due under the October 2020 Lease agreement, as amended, as of March 31, 2024 are as follows (in thousands): 2024 $ 49 Total remaining lease payments 49 Less: imputed lease interest (1 ) Less: Current portion (48 ) Operating lease liability, net of current portion $ — Rent expense, which is included in general and administrative expense, for the three months ended March 31, 2024 and 2023 was $22,000 and $31,000, respectively. As of March 31, 2024, the lease liability was $48,000, it is all current and is included in accrued expenses and other liabilities in the accompanying balance sheet. Cash paid for amounts included in the measurement of lease liabilities and the operating cash flows from operating leases for the three months ended March 31, 2024 and 2023 were $23,000 and $33,000, respectively. The weighted -average Patent Agreement In July 2021, ARCA entered into a patent assignment agreement (the “Agreement”) with the University Medical Center of Johannes Gutenberg University Mainz, Germany. Under the terms of the Agreement, ARCA received exclusive world -wide -19 -Prof	(6) Commitments and Contingencies ARCA has or is subject to the following commitments and contingencies: Employment Agreements and Reduction of Workforce ARCA maintains employment agreements with several key executive employees. The agreements may be terminated at any time by ARCA with or without cause upon written notice to the employee, and entitle the employee to wages in lieu of notice for periods not exceeding one calendar year from date of termination without cause or by the employee for good reason. Certain of these agreements also provide for payments to be made under certain conditions related to a change in control of ARCA. In December 2022, ARCA’s Board of Directors approved retention bonuses for certain employees, subject to continued employment with ARCA through the earlier of a change in control of ARCA or certain clinical development decisions totaling $265,000. In November 2023, the retention bonuses were amended to increase the aggregate amount of the retention bonus by 50% and in order to assist with tax obligations associated with the vesting of certain Company restricted stock unit awards in December 2023, a total of $86,000 was paid in December 2023. As of December 31, 2023, the unpaid retention bonuses totaled $311,000, none of which was accrued as of December 31, 2023, since there had not been a change in control or clinical development decision. ARCA and Christopher D. Ozeroff, the Secretary, Senior Vice President and General Counsel of ARCA mutually agreed to conclude Mr. Ozeroff’s employment effective March 31, 2023. Pursuant to Mr. Ozeroff’s existing employment agreement, as previously amended, ARCA will provide Mr. Ozeroff severance benefits pursuant to the terms of his existing employment agreement with ARCA, as previously amended. The severance benefits include severance payments and reimbursement to cover out -of-pocket -of-pocket none In 2022, ARCA implemented a strategic reduction of the workforce by approximately 67%, or 12 employees. Personnel reductions were primarily focused in research and development and general and administrative functions. The restructuring was a result of ARCA’s decision to manage operating costs and expenses. During the year ended December 31, 2022, ARCA recorded total restructuring charges of approximately $755,000, of which $470,000 and $285,000 were recognized in research and development and general and administrative expenses, respectively, in connection with the restructuring, all in the form of one -time Operating Lease On August 29, 2020 ARCA entered into a lease agreement for approximately 5,200 square feet of office facilities in Westminster, Colorado which serves as ARCA’s primary business office effective October 1, 2020 (“October 2020 Lease”). The lease term is 42 months beginning October 1, 2020 and includes an option to renew for an additional 36 -lease Future minimum commitments due under the October 2020 Lease agreement as of December 31, 2023 are as follows (in thousands): 2024 $ 93 2025 96 2026 100 2027 25 Total remaining lease payments 314 Less: imputed lease interest (34 ) Less: Current portion (76 ) Operating lease liability, net of current portion $ 204 Rent expense, which is included in general and administrative expense, under these leases for the years ended December 31, 2023 and 2022 was $119,000 and $125,000, respectively. As of December 31, 2023, the lease liability was $280,000 and the current portion is included in accrued expenses and other liabilities and the non -current -average -average Patent Agreement In July 2021, ARCA entered into a patent assignment agreement (the “Agreement”) with the University Medical Center of Johannes Gutenberg University Mainz, Germany. Under the terms of the Agreement, ARCA received exclusive world -wide -19 -Prof Gencaro License ARCA has licensed worldwide rights to all preclinical and clinical data through the BEST trial for development of bucindolol. The patents that were the subject of this license are expired. If the license agreement is deemed enforceable, ARCA would incur milestone and royalty obligations upon the occurrence of certain events, including if the FDA grants marketing approval for Gencaro, upon regulatory marketing approval in Europe and Japan and based on achievement of specified product sales levels.

Equity Financings

Equity Financings	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Equity Financings [Abstract]
Equity Financings	(7) Equity Financings At the Market Equity Financing In 2020, ARCA entered into a Capital on Demand™ Sales Agreement (the “Sales Agreement”) with JonesTrading Institutional Services LLC, as agent (“JonesTrading”), pursuant to which ARCA may offer and sell, from time to time through JonesTrading, shares of ARCA’s common stock, par value $0.001 per share (“ARCA common stock”). In 2021, ARCA amended the 2020 Sales Agreement and the amount available for the offering under its prospectus to ARCA’s registration statement on Form S -3 -254585 No sales were made under the Sales Agreement in 2024 or 2023. Merger Agreement See “Financing Transaction” discussion in Note 10 below.	(7) Equity Financings At the Market Equity Financing On July 22, 2020, ARCA entered into a Capital on Demand TM Under the Sales Agreement, JonesTrading may sell the Shares by any method permitted by law and deemed to be an “at the market offering” as defined in Rule 415 promulgated under the Securities Act of 1933, as amended, including sales made directly on or through the Nasdaq Capital Market, on any other existing trading market for ARCA common stock or to or through a market maker. In addition, under the amended Sales Agreement, JonesTrading may sell the Shares by any other method permitted by law, including in negotiated transactions. ARCA may instruct JonesTrading not to sell Shares if the sales cannot be effected at or above the price designated by ARCA from time to time. ARCA is not obligated to make any sales of the Shares under the Sales Agreement. The offering of Shares pursuant to the Sales Agreement will terminate upon the earlier of (a) the sale of all of the Shares subject to the Sales Agreement or (b) the termination of the Sales Agreement by JonesTrading or ARCA, as permitted therein. ARCA paid JonesTrading a commission rate equal to 3.0% of the aggregate gross proceeds from each sale of Shares and agreed to provide JonesTrading with customary indemnification and contribution rights. ARCA will also reimburse JonesTrading for certain specified expenses in connection with entering into the Sales Agreement. No sales were made in 2023 or 2022. In April 2021, ARCA amended the 2020 Sales Agreement and the amount available for the offering under its prospectus to ARCA’s registration statement on Form S -3 -254585 -third -month

Share-based Compensation

Share-based Compensation	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Share-Based Payment Arrangement [Abstract]
Share-based Compensation	(8) Share-based Compensation For the three months ended March 31, 2024 and 2023, ARCA recognized the following non -cash -based Three Months Ended 2024 2023 General and administrative $ 114 $ 163 Research and development — 41 Total $ 114 $ 204 Stock option transactions for the three months ended March 31, 2024 under ARCA’s stock incentive plans were as follows: Options Outstanding Number of Weighted Weighted Options outstanding – December 31, 2023 616,707 $ 4.76 7.35 Granted 42,000 1.64 Exercised — — Forfeited and cancelled (12,862 ) 17.45 Options outstanding – March 31, 2024 645,845 $ 4.30 6.82 Options exercisable – March 31, 2024 502,517 $ 4.71 6.55 Options vested and expected to vest – March 31, 2024 645,816 $ 4.30 6.82	(8) Share-based Compensation Stock Plans ARCA’s equity incentive plan, the 2020 Equity Incentive Plan The Equity Plan provides for the granting of stock options (including indexed options), restricted stock units, stock appreciation rights, restricted stock purchase rights, restricted stock bonuses, performance shares, performance units and deferred stock units. Under the Equity Plan, awards may be granted to employees, directors and consultants of ARCA, except for incentive stock options, which may be granted only to employees. As of December 31, 2023, options to purchase 601,900 In general, the Equity Plan authorizes the grant of stock options that vest at rates set by the Board of Directors or the Compensation Committee thereof. Generally, stock options granted by ARCA under the equity incentive plans become exercisable ratably for a period of three four ten In conjunction with the adoption of the Equity Plan, ARCA discontinued grants under the 2013 Plan, effective December 10, 2020. As of December 31, 2023, options to purchase 14,807 ARCA did not grant options in 2023. ARCA granted options to purchase an aggregate of 60,000 -Scholes Year Ended Expected term 5.5 years Expected volatility 107 % Risk-free interest rate 3.56 % Expected dividend yield 0 % Weighted-average grant date fair value per share $ 1.87 A summary of ARCA’s stock option activities for the years ended December 31, 2023 and 2022, and related information as of December 31, 2023, is as follows: Options Outstanding Number of Weighted Weighted Aggregate Options outstanding – December 31, 2021 904,123 $ 5.59 Granted 60,000 2.31 Exercised — — Forfeited and cancelled (259,163 ) 4.74 Options outstanding – December 31, 2022 704,960 $ 5.62 8.29 $ 18 Granted — — Exercised — — Forfeited and cancelled (88,253 ) 11.68 Options outstanding – December 31, 2023 616,707 $ 4.76 7.35 $ — Options exercisable – December 31, 2023 463,068 $ 5.28 7.29 $ — Options vested and expected to vest – December 31, 2023 616,661 $ 4.76 7.35 $ — The aggregate intrinsic value in the table above represents the total intrinsic value, based on ARCA’s closing price as of December 31 of the respective year, which would have been received by the option holders had all the option holders with in -the-money -based -line Restricted Stock Units ARCA granted restricted stock units (“RSUs”) under the Equity Plan to employees during 2022. The fair value of RSU awards is the closing price of ARCA common stock on the date of the grant and is recognized as compensation expense on a straight -line one A summary of RSU activity for the year ended December 31, 2023 is presented below: Restricted Stock Units Number of Weighted RSUs outstanding – December 31, 2021 — $ — Granted 91,000 2.21 Vested and released — — Forfeited and cancelled — — RSUs outstanding – December 31, 2022 91,000 $ 2.21 Granted — — Vested and released (91,000 ) 2.21 Forfeited and cancelled — — RSUs outstanding – December 31, 2023 — $ — As of December 31, 2023, there was no unrecognized compensation cost related to unvested stock awards. Non-cash Stock-based Compensation For the years ended December 31, 2023 and 2022, ARCA recognized the following non -cash -based Years Ended 2023 2022 General and administrative $ 526 $ 423 Research and development 160 133 Total $ 686 $ 556 ARCA did not recognize any tax benefit related to employee stock -based

Employee Benefit Plans

Employee Benefit Plans	12 Months Ended
	Dec. 31, 2023
Employee Benefit Plans [Abstract]
Employee Benefit Plans	(9) Employee Benefit Plans ARCA has a 401(k) plan and makes a matching contribution equal to 100% of the employee’s first 3% of the employee’s contributions and 50% of the employee’s next 2% of contributions. ARCA adopted the plan in 2006 and contributed $56,000 and $96,000 for the years ended December 31, 2023 and 2022, respectively.

Income Taxes

Income Taxes	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Income Taxes [Abstract]
Income Taxes	(9) Income Taxes In accordance with GAAP, a valuation allowance should be provided if it is more likely than not that some or all of ARCA’s deferred tax assets will not be realized. ARCA’s ability to realize the benefit of its deferred tax assets will depend on the generation of future taxable income. Due to the uncertainty of future profitable operations and taxable income, ARCA has recorded a full valuation allowance against its net deferred tax assets. ARCA believes its tax filing positions and deductions related to tax periods subject to examination will be sustained upon audit and, therefore, has no	( 10) Income Taxes Effective June 1, 2005, ARCA changed from an S -Corporation -Corporation -Corporation 2025 2037 carryforwards accumulated from June 2005 to the change in ownership date will be subject to annual limitations to offset future taxable income. The annual limitation may result in the expiration of the net operating losses and credits before utilization. As such, a portion of ARCA’s net operating loss carryforwards may be limited. In assessing the realizability of deferred tax assets, management considers whether it is more likely than not that some portion or all of the deferred tax assets will not be realized. The ultimate realization of deferred tax assets is dependent upon the generation of future taxable income during the period in which those temporary differences become deductible. Management considers the scheduled reversal of deferred tax liabilities, projected future taxable income and tax planning strategies in making this assessment. Due primarily to ARCA’s history of operating losses, management is unable to conclude that it is more likely than not that ARCA will realize the benefits of these deductible differences, and accordingly has provided a valuation allowance against the entire net deferred tax assets and liabilities of approximately $55.5 million at December 31, 2023, reflecting an increase of approximately $1.2 million from December 31, 2022. The deferred tax assets are primarily comprised of net operating loss carryforwards and research and experimentation credit carryforwards. As of December 31, 2023, ARCA has not performed an Internal Revenue Code Section 382 limitation study. Depending on the outcome of such a study, the gross amount of net operating losses recognizable in future tax periods could be limited. A limitation in the carryforwards would decrease the carrying amount of the gross amount of the net operating loss carryforwards, with a corresponding decrease in the valuation allowance recorded against these gross deferred tax assets. Income tax benefit attributable to ARCA’s loss from operations before income taxes differs from the amounts computed by applying the U.S. federal statutory income tax rate of 21% for 2023 and 2022, as a result of the following (in thousands): Years ended 2023 2022 U.S. federal income tax benefit at statutory rates $ (1,121 ) $ (2,085 ) State income tax benefit, net of federal benefit (192 ) (357 ) Research and experimentation credits — — Deferred tax asset adjustment 47 2 Other 107 186 Change in valuation allowance 1,159 2,254 Income tax benefit $ — $ — Deferred income taxes reflect the net tax effects of temporary differences between the carrying amounts of assets and liabilities for financial reporting and the amounts used for income tax purposes, as well as operating loss and tax credit carryforwards. The income tax effects of temporary differences and carryforwards that give rise to significant portions of ARCA’s net deferred tax assets and liabilities consisted of the following (in thousands): As of December 31, 2023 2022 Deferred tax assets: Net operating loss carryforwards $ 51,190 $ 50,008 Charitable contribution carryforwards 371 393 Research and experimentation credits 2,420 2,420 Capitalized research and development costs 951 979 Capitalized intangibles 354 356 Stock-based compensation 232 205 Accrued compensation 7 6 Lease liabilities 69 94 Total deferred tax assets 55,594 54,461 Valuation allowance (55,531 ) (54,372 ) Deferred tax assets, net of valuation allowance 63 89 Deferred tax liabilities: Right-of-use asset (61 ) (84 ) Depreciation and amortization (2 ) (5 ) Net deferred tax liability $ — $ — Since ARCA is in a loss carryforward position, it is generally subject to U.S. federal and state income tax examinations by tax authorities for all years for which a loss carryforward is available. Thus, ARCA’s open tax years extend back to 2009

Subsequent Events

Subsequent Events	3 Months Ended
	Mar. 31, 2024
Subsequent Events [Abstract]
Subsequent Events	(10) Subsequent Events Merger Agreement On April 3, 2024, ARCA, Merger Sub I, Merger Sub II and Oruka, entered into the Merger Agreement, pursuant to which, among other matters, and subject to the satisfaction or waiver of the conditions set forth in the Merger Agreement, Merger Sub I will merge with and into Oruka, with Oruka continuing as a wholly owned subsidiary of ARCA and the surviving corporation of the merger and as part of the same overall transaction, the surviving corporation in the First Merger will merge with and into Merger Sub II with Merger Sub II continuing as a wholly owned subsidiary of ARCA and the surviving entity of the merger. The Merger is intended to qualify for federal income tax purposes as a tax -free Subject to the terms and conditions of the Merger Agreement, at the closing of the First Merger, (a) each then -outstanding -outstanding -outstanding -outstanding Under the Exchange Ratio formula in the Merger Agreement, upon the closing of the First Merger, on a pro forma basis and based upon the number of shares of ARCA common stock expected to be issued in the First Merger, pre -First -funded -First adjusted to the extent that ARCA’s net cash at closing is less than $5.0 million and will be based on the amount of proceeds actually received by Oruka in the financing transaction described below, as further described in the Merger Agreement. In addition, prior to the closing of the First Merger, ARCA expects to declare a cash dividend to the pre -First In connection with the Merger, ARCA is required to seek the approval of its stockholders to, among other things, (a) issue shares of ARCA common stock issuable in connection with the First Merger (including the shares of ARCA common stock issuable under the Series B Preferred Stock) under the rules of Nasdaq, and (b) amend its amended and restated certificate of incorporation, to (i) effect a reverse stock split of ARCA common stock (if deemed necessary by ARCA and Oruka), (ii) increase the number of shares of ARCA common stock that ARCA is authorized to issue, and (iii) such other changes as are mutually agreeable to ARCA and Oruka (the “ARCA Voting Proposals”). Each of ARCA and Oruka has agreed to customary representations, warranties and covenants in the Merger Agreement, including, among others, covenants relating to (1) using commercially reasonable efforts to obtain the requisite approval of its stockholders, (2) non -solicitation Consummation of the Merger is subject to certain closing conditions, including, among other things, (1) approval by ARCA stockholders of the ARCA Voting Proposals, (2) approval by the requisite Oruka stockholders of the adoption and approval of the Merger Agreement and the transactions contemplated thereby, (3) Nasdaq’s approval of the initial listing application to be submitted in connection with the First Merger, (4) the effectiveness of the Registration Statement, (5) the expiration of any applicable waiting periods (or extensions thereof) under the Hart Scott -Rodino -First -First The Merger Agreement contains certain termination rights of each of ARCA and Oruka. Upon termination of the Merger Agreement under specified circumstances, ARCA and Oruka may each be required to pay the other party a termination fee of $440,000. Pursuant to a Certificate of Designation of Preferences, Rights and Limitations of the Series B Non -Voting -Voting -if-converted-to-ARCA basis, and in the same form as dividends actually paid on shares of the ARCA common stock. Except as otherwise required by the Certificate of Designation or law, the Series B Preferred Stock will not have voting rights. However, as long as any shares of Series B Preferred Stock are outstanding, ARCA will not, without the affirmative vote of the holders of a majority of the then outstanding shares of the Series B Preferred Stock, (a) alter or change adversely the powers, preferences or rights given to the Series B Preferred Stock, (b) alter or amend the Certificate of Designation, (c) amend its certificate of incorporation, bylaws or other charter documents in any manner that adversely affects any rights of the holders of the Series B Preferred Stock, (d) file any articles of amendment, certificate of designations, preferences, limitations and relative rights of any series of Preferred Stock (as defined in the Certificate of Designation), if such action would adversely alter or change the preferences, rights, privileges or powers of, or restrictions provided for the benefit of the Series B Preferred Stock, (e) issue further shares of the Series B Preferred Stock or increase or decrease (other than by conversion) the number of authorized shares of the Series B Preferred Stock, (f) at any time while at least 30% of the originally issued Series B Preferred Stock remains issued and outstanding, consummate either (A) a Fundamental Transaction (as defined in the Certificate of Designation) or (B) any merger or consolidation of ARCA or other business combination in which the stockholders of ARCA immediately before such transaction do not hold at least a majority of the capital stock of ARCA immediately after such transaction, or (f) enter into any agreement with respect to any of the foregoing. The Series B Preferred Stock does not have a preference upon any liquidation, dissolution or winding -up Following the closing of the First Merger, each share of Series B Preferred Stock then outstanding shall be convertible, at any time and from time to time, at the option of the holder of the Series B Preferred Stock, into a number of shares equal to 1,000 At the effective time of the First Merger (the “First Effective Time”), the combined company’s board of directors is expected to consist of five (5) members, all of whom will be designated by Oruka. Upon the closing of the transaction, the combined company will be led by Oruka’s chief executive officer. Financing Transaction Concurrently with the execution and delivery of the Merger Agreement, certain parties have entered into a subscription agreements with Oruka, pursuant to which they have agreed, subject to the terms and conditions of such agreements, to purchase immediately prior to the consummation of the First Merger, shares of Oruka common stock and pre -funded -funded -funded Separation of Michael Bristow, M.D., President, Chief Executive Officer and Director Effective April 3, 2024, ARCA and Dr. Michael Bristow, President, Chief Executive Officer and a member of the Board mutually agreed to conclude Dr. Bristow’s employment and service as a director. In connection with Dr. Bristow’s separation, ARCA and Dr. Bristow entered into a separation agreement (the “Separation Agreement”) on April 3, 2024. Pursuant to the terms of the Separation Agreement, ARCA provided to Dr. Bristow a lump sum payment equal to (i) twelve (12) months of Dr. Bristow’s base salary as of the last date of his employment and (ii) a cash payment of $25,000, less applicable withholdings. The severance benefits were conditioned on the non -revocation ARCA and Dr. Bristow entered into a consulting agreement, effective April 3, 2024 (the “Consulting Agreement”), pursuant to which Dr. Bristow is providing certain consulting services provided for in the Consulting Agreement to ARCA until the earlier of (i) the completion of services under the Consulting Agreement, (ii) a termination in accordance with the terms of the Consulting Agreement, and (iii) upon a Change of Control (as defined in ARCA’s 2020 Equity Incentive Plan (the “Plan”)). Pursuant to the Consulting Agreement, Dr. Bristow provision of services under the Consulting Agreement are deemed to be a Continuous Service (as defined in the Plan) and, as a result, his equity awards under the Plan continue to vest during the term of the Consulting Agreement. Appointment of Thomas Keuer as President Effective as of April 3, 2024, the Board appointed Thomas A. Keuer, ARCA’s Chief Operating Officer, to serve as ARCA’s President and principal executive officer. Mr. Keuer has been with ARCA since 2006, and as its Chief Operating Officer for the last nine years, a position he will continue to serve in. Mr. Keuer will not receive any additional compensation in connection with his appointment as President and principal executive officer. Mr. Keuer’s position will end upon closing of the merger transaction with Oruka Therapeutics, Inc. as previously disclosed on a Current Report on Form 8 -K Second Amendment to Retention Bonus Letter of Thomas A. Keuer and C. Jeffrey Dekker On April 20, 2024, the board of directors of ARCA approved the second amendment of certain retention bonus letters between ARCA and each of Thomas A. Keuer and C. Jeffrey Dekker to increase the aggregate amount of the retention bonus with respect to each such executive to $200,000. The remaining portion of the retention bonus with respect to Thomas A. Keuer and C. Jeffrey Dekker, consisting of $165,000, will become payable consistent with the original terms of the applicable retention bonus letter and first amendment to retention bonus letter. Any payment related to the retention bonuses of Thomas A. Keuer and C. Jeffrey Dekker will be paid by ARCA via payroll within 30 business days of the date of occurrence of the applicable “Payment Event Date” (as such term is otherwise defined in the applicable second amendment to the retention bonus letter). Each such retention bonus letter and first amendment to retention bonus letter will otherwise remain subject to their original terms and conditions.

Accounting Policies, by Policy

Accounting Policies, by Policy (Policies)	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
ARCA and Summary of Significant Accounting Policies [Abstract]
Description of Business	Description of Business ARCA biopharma, Inc. (“ARCA”), a Delaware corporation, is headquartered in Westminster, Colorado. ARCA is dedicated to applying a precision medicine approach to the development and commercialization of genetically targeted therapies for cardiovascular diseases. ARCA’s lead product candidate is Gencaro™ (bucindolol hydrochloride) for the treatment of atrial fibrillation (“AF”) in patients with chronic heart failure (“HF”). In April 2022, ARCA established a Special Committee of the board of directors (the “Board”) of ARCA to conduct a comprehensive review of strategic alternatives. As part of the strategic review process, ARCA explored potential strategic alternatives that included, without limitation, an acquisition, merger, business combination or other transactions. ARCA has and is continuing to explore strategic alternatives related to its product candidates and related assets, including, without limitation, licensing transactions and asset sales. On April 3, 2024, following a comprehensive review of strategic alternatives, ARCA, Atlas Merger Sub Corp., a Delaware corporation and a wholly -owned -owned ” -free ARCA’s future operations are highly dependent on the success of the Merger and there can be no assurances that the Merger will be successfully consummated. In the event that ARCA does not complete the Merger, it may explore strategic alternatives, including, without limitation, another strategic transaction and/or pursue a dissolution and liquidation of ARCA. See Note 10.	Description of Business ARCA biopharma, Inc. (“ARCA”), a Delaware corporation, is headquartered in Westminster, Colorado. ARCA is a clinical -stage In April 2022, the Board of Directors established a Special Committee and, in May 2022, retained Ladenburg Thalmann & Co. Inc. to evaluate strategic options, including transactions involving a merger, sale of all or part of ARCA’s assets, or other alternatives with the goal of maximizing stockholder value. ARCA does not have a defined timeline for the strategic review process and the review may not result in any specific action or transaction.
Liquidity and Going Concern	Liquidity and Going Concern ARCA devotes substantially all of its efforts towards obtaining regulatory approval and raising capital necessary to fund its operations and it is subject to a number of risks associated with clinical research and development, including dependence on key individuals, the development of and regulatory approval of commercially viable products, the need to raise adequate additional financing necessary to fund the development and commercialization of its products, and competition from larger companies. ARCA has not generated revenue to date and has incurred substantial losses and negative cash flows from operations since its inception. ARCA has historically funded its operations through issuances of common and preferred stock. ARCA believes that its current cash and cash equivalents as of March 31, 2024 will be sufficient to fund its operations through the middle of fiscal year 2025. The future viability of ARCA beyond that point is dependent on the results of the strategic review process and its ability to raise additional capital to fund its operations. ARCA expects to continue to incur costs and expenditures in connection with the process of evaluating strategic alternatives. There can be no assurance, however, that ARCA will be able to successfully consummate any particular strategic transaction, including the Merger Agreement. The process of continuing to evaluate these strategic options may be very costly, time -consuming able to execute any strategic transaction. Changing circumstances may cause ARCA to consume capital significantly faster or slower than currently anticipated. ARCA has based these estimates on assumptions that may prove to be wrong, and it could exhaust its available financial resources sooner than it currently anticipates. Depending on the results of the strategic review process, ARCA may have to raise additional capital for clinical trials of Gencaro and to fund its operations. ARCA may not be able to raise sufficient capital on acceptable terms, or at all, to continue development of Gencaro or rNAPc2 or to otherwise continue operations and may not be able to execute any strategic transaction. ARCA’s liquidity, and its ability to raise additional capital or complete any strategic transaction, depends on a number of factors, including, but not limited to, the following: • • • • • • • • • The sale of additional equity or convertible debt securities would likely result in substantial additional dilution to ARCA’s stockholders. If ARCA raises additional funds through the incurrence of indebtedness, the obligations related to such indebtedness would be senior to rights of holders of ARCA’s capital stock and could contain covenants that would restrict ARCA’s operations. ARCA also cannot predict what consideration might be available, if any, to it or its stockholders, in connection with any strategic transaction. Should strategic alternatives or additional capital not be available to ARCA, or not be available on acceptable terms, ARCA may be unable to realize value from its assets and discharge its liabilities in the normal course of business which may, among other alternatives, cause ARCA to further delay, substantially reduce or discontinue operational activities to conserve its cash resources.	Liquidity and Going Concern ARCA devotes substantially all of its efforts towards obtaining regulatory approval and raising capital necessary to fund its operations and it is subject to a number of risks associated with clinical research and development, including dependence on key individuals, the development of and regulatory approval of commercially viable products, the need to raise adequate additional financing necessary to fund the development and commercialization of its products, and competition from larger companies. ARCA has not generated revenue to date and has incurred substantial losses and negative cash flows from operations since its inception. ARCA has historically funded its operations through issuances of common and preferred stock. ARCA believes that its current cash and cash equivalents as of December 31, 2023 will be sufficient to fund its operations through the middle of fiscal year 2025. ARCA’s review of its strategic options may impact this projection. Changing circumstances may cause ARCA to consume capital significantly faster or slower than currently anticipated. ARCA has based these estimates on assumptions that may prove to be wrong, and ARCA could exhaust its available financial resources sooner than it currently anticipates. Therefore, ARCA will have to raise additional capital for clinical trials of Gencaro. ARCA may not be able to raise sufficient capital on acceptable terms, or at all, to continue development of Gencaro or rNAPc2 or to otherwise continue operations and may not be able to execute any strategic transaction. ARCA’s liquidity, and its ability to raise additional capital or complete any strategic transaction, depends on a number of factors, including, but not limited to, the following: • • • • • • • The sale of additional equity or convertible debt securities would likely result in substantial additional dilution to ARCA’s stockholders. If ARCA raises additional funds through the incurrence of indebtedness, the obligations related to such indebtedness would be senior to rights of holders of ARCA’s capital stock and could contain covenants that would restrict ARCA’s operations. ARCA also cannot predict what consideration might be available, if any, to it or its stockholders, in connection with any strategic transaction. Should strategic alternatives or additional capital not be available to ARCA, or not be available on acceptable terms, ARCA may be unable to realize value from its assets and discharge its liabilities in the normal course of business which may, among other alternatives, cause ARCA to further delay, substantially reduce or discontinue operational activities to conserve its cash resources.
Basis of Presentation	Basis of Presentation The accompanying unaudited financial statements of ARCA were prepared in accordance with generally accepted accounting principles for interim financial information and pursuant to Regulation S -X strategic alternatives for further developing and commercializing Gencaro and rNAPc2, and raising capital. These unaudited financial statements should be read in conjunction with the audited financial statements and footnotes thereto for the year ended December 31, 2023 included elsewhere in this proxy statement/prospectus. Amounts presented are rounded to the nearest thousand, where indicated, except per share data and par values.	Basis of Presentation The accompanying financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“GAAP”) and include all adjustments necessary for the fair presentation of ARCA’s financial position, results of operations and cash flows for the periods presented. Management has performed an evaluation of ARCA’s activities through the date of filing of the Annual Report on Form 10 -K
Recent Accounting Pronouncements	Recent Accounting Pronouncements ARCA reviewed recently issued accounting pronouncements and concluded that they were either not applicable or not expected to have a significant impact to the financial statements.	Recent Accounting Pronouncements ARCA reviewed all other recently issued accounting pronouncements and concluded that they were either not applicable or not expected to have a significant impact to the financial statements.
Accounting Estimates in the Preparation of Financial Statements		Accounting Estimates in the Preparation of Financial Statements The preparation of financial statements in conformity with accounting principles generally accepted in the United States of America requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of expenses during the reporting period. ARCA bases estimates on various assumptions that are believed to be reasonable under the circumstances. ARCA believes significant judgment was involved in estimating the outsourcing expenses, and in estimating other accrued liabilities and income taxes. Management is continually evaluating and updating these estimates, and it is possible that these estimates will change in the future or that actual results may differ from these estimates.
Cash Equivalents		Cash Equivalents Cash equivalents generally consist of money market funds and debt securities with maturities of 90 days or less at the time of purchase. ARCA invests its excess cash in securities with strong ratings and has established guidelines relative to diversification and maturity with the objective of maintaining safety of principal and liquidity.
Concentrations of Credit Risk	Concentrations of Credit Risk Financial instruments that potentially subject ARCA to significant concentrations of credit risk consist primarily of cash and cash equivalents. ARCA has no off -balance-sheet	Concentrations of Credit Risk Financial instruments that potentially subject ARCA to significant concentrations of credit risk consist primarily of cash and cash equivalents. ARCA has no off -balance-sheet
Property and Equipment		Property and Equipment Property and equipment are stated at cost less accumulated depreciation and amortization. Cost includes expenditures for equipment, leasehold improvements, replacements, and renewals. Maintenance and repairs are charged to expense as incurred. When assets are sold, retired, or otherwise disposed of, the cost and accumulated depreciation are removed from the accounts and any resulting gain or loss is reflected in operations. The cost of property and equipment is depreciated using the straight -line
Comprehensive Loss	Comprehensive Loss Comprehensive loss is defined as the change in equity during a period from transactions and other events and/or circumstances from non -owner	Comprehensive Loss Comprehensive loss is defined as the change in equity during a period from transactions and other events and/or circumstances from non -owner
Leases	Leases ARCA determines if an arrangement is a lease at inception. Operating leases are included in right -of-use ROU lease assets represent ARCA’s right to use an underlying asset for the lease term and lease obligations represent ARCA’s obligation to make lease payments arising from the lease. Operating ROU lease assets are recognized at the commencement date based on the present value of lease payments over the lease term. As ARCA’s leases do not provide an implicit rate, ARCA uses its incremental borrowing rate based on the information available at the commencement date in determining the present value of lease payments. ARCA’s lease terms may include options to extend or terminate a lease when it is reasonably certain that ARCA will exercise that option. Lease expense for lease payments is recognized on a straight -line	Leases ARCA determines if an arrangement is a lease at inception. Operating leases are included in right -of-use ROU lease assets represent ARCA’s right to use an underlying asset for the lease term and lease obligations represent ARCA’s obligation to make lease payments arising from the lease. Operating ROU lease assets are recognized at the commencement date based on the present value of lease payments over the lease term. As ARCA’s lease does not provide an implicit rate, ARCA uses its incremental borrowing rate based on the information available at the commencement date in determining the present value of lease payments. ARCA’s lease terms may include options to extend or terminate the lease when it is reasonably certain that ARCA will exercise that option. Lease expense for lease payments is recognized on a straight -line
Accrued Outsourcing Expenses	Accrued Outsourcing Expenses As part of the process of preparing its financial statements, ARCA is required to estimate accrued outsourcing expenses. This process involves identifying services that third parties have performed on ARCA’s behalf and estimating the level of service performed and the associated cost incurred for these services as of the balance sheet date. Examples of estimated accrued outsourcing expenses include contract service fees, such as fees payable to contract manufacturers in connection with the production of materials related to ARCA’s drug product, and service fees and pass through costs from clinical research organizations. ARCA develops estimates of liabilities using its judgment based upon the facts and circumstances known at the time.	Accrued Outsourcing Expenses As part of the process of preparing its financial statements, ARCA is required to estimate accrued outsourcing expenses. This process involves identifying services that third parties have performed on ARCA’s behalf and estimating the level of service performed and the associated cost incurred for these services as of the balance sheet date. Examples of estimated accrued outsourcing expenses include contract service fees, such as fees payable to contract manufacturers in connection with the production of materials related to ARCA’s drug product, and service fees and pass through costs from clinical research organizations. ARCA develops estimates of liabilities using its judgment based upon the facts and circumstances known at the time.
Segments		Segments ARCA operates in one segment. Management uses one measure of profitability and does not segment its business for internal reporting.
Research and Development		Research and Development Research and development costs are expensed as incurred. These consist primarily of salaries, contract services, and supplies. Costs, if any, related to clinical trial and drug manufacturing activities are based upon estimates of the services received and related expenses incurred by contract research organizations (“CROs”), clinical study sites, drug manufacturers, collaboration partners, laboratories, consultants, or otherwise. Related contracts vary significantly in length, and could be for a fixed amount, a variable amount based on actual costs incurred, capped at a certain limit, or for a combination of these elements. Activity levels are monitored through communications with the vendors, including detailed invoices and task completion review, analysis of expenses against budgeted amounts, and pre -approval an estimate of costs incurred but not invoiced on a periodic basis. Expenses related to the CROs and clinical studies, as well as contract drug manufacturers, are primarily based on progress made against specified milestones or targets in each period. In accordance with certain research and development agreements, ARCA is obligated to make certain upfront payments upon execution of the agreement. ARCA records these upfront payments as prepaid research and development expenses, which are included in Other current assets or Other assets in the accompanying Balance Sheets. Such payments are recorded to research and development expense as services are performed. ARCA evaluates on a quarterly basis whether events and circumstances have occurred that may indicate impairment of remaining prepaid research and development expenses.
Stock-Based Compensation		Stock-Based Compensation ARCA’s stock -based -based -line
Income Taxes		Income Taxes The current benefit for income taxes represents actual or estimated amounts payable or refundable on tax returns filed or to be filed each year. Deferred tax assets and liabilities are recognized for the estimated future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases and operating loss and tax credit carryforwards. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in the period that includes the enactment date. The overall change in deferred tax assets and liabilities for the period measures the deferred tax expense or benefit for the period. The measurement of deferred tax assets may be reduced by a valuation allowance based on judgmental assessment of available evidence if deemed more likely than not that some or all of the deferred tax assets will not be realized.

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Net Loss Per Share [Abstract]
Schedule of Potentially Dilutive Shares of Common Stock	Because ARCA reported a net loss for the three months ended March 31, 2024 and 2023, all potentially dilutive shares of ARCA common stock have been excluded from the computation of the dilutive net loss per share for all periods presented. Such potentially dilutive shares of ARCA common stock consist of the following: March 31, 2024 2023 Potentially dilutive securities, excluded: Outstanding stock options 645,845 664,857 Unvested restricted stock units — 91,000 645,845 755,857	Because ARCA reported a net loss for the years ended December 31, 2023 and 2022, all potentially dilutive shares of ARCA common stock have been excluded from the computation of the dilutive net loss per share for all periods presented. Such potentially dilutive shares of ARCA common stock consist of the following: Years Ended 2023 2022 Potentially dilutive securities, excluded: Outstanding stock options 616,707 704,960 Unvested restricted stock units — 91,000 616,707 795,960

Property and Equipment (Tables)

Property and Equipment (Tables)	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Property and Equipment [Abstract]
Schedule of Property and Equipment	Property and equipment consist of the following (in thousands): Estimated March 31, December 31, Computer equipment 3 years $ 39 $ 39 Lab equipment 5 years 130 130 Furniture and fixtures 5 years 37 37 Computer software 3 years 16 16 222 222 Accumulated depreciation and amortization (215 ) (212 ) Property and equipment, net $ 7 $ 10	Property and equipment consist of the following (in thousands): Estimated December 31, December 31, Computer equipment 3 years $ 39 $ 39 Lab equipment 5 years 130 130 Furniture and fixtures 5 years 37 44 Computer software 3 years 16 16 222 229 Accumulated depreciation and amortization (212 ) (204 ) Property and equipment, net $ 10 $ 25

Commitments and Contingencies (

Commitments and Contingencies (Tables)	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Commitments and Contingencies Disclosure [Abstract]
Schedule of Future Minimum Commitments Due	Future minimum commitments due under the October 2020 Lease agreement, as amended, as of March 31, 2024 are as follows (in thousands): 2024 $ 49 Total remaining lease payments 49 Less: imputed lease interest (1 ) Less: Current portion (48 ) Operating lease liability, net of current portion $ —	Future minimum commitments due under the October 2020 Lease agreement as of December 31, 2023 are as follows (in thousands): 2024 $ 93 2025 96 2026 100 2027 25 Total remaining lease payments 314 Less: imputed lease interest (34 ) Less: Current portion (76 ) Operating lease liability, net of current portion $ 204

Share-based Compensation (Table

Share-based Compensation (Tables)	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Share-Based Payment Arrangement [Abstract]
Schedule of Estimated Weighted Average Grant Date Fair Value Per Share		The fair values of employee stock options granted in the year ended December 31, 2022 were estimated at the date of grant using the Black -Scholes Year Ended Expected term 5.5 years Expected volatility 107 % Risk-free interest rate 3.56 % Expected dividend yield 0 % Weighted-average grant date fair value per share $ 1.87
Schedule of Stock Option Activities	Stock option transactions for the three months ended March 31, 2024 under ARCA’s stock incentive plans were as follows: Options Outstanding Number of Weighted Weighted Options outstanding – December 31, 2023 616,707 $ 4.76 7.35 Granted 42,000 1.64 Exercised — — Forfeited and cancelled (12,862 ) 17.45 Options outstanding – March 31, 2024 645,845 $ 4.30 6.82 Options exercisable – March 31, 2024 502,517 $ 4.71 6.55 Options vested and expected to vest – March 31, 2024 645,816 $ 4.30 6.82	A summary of ARCA’s stock option activities for the years ended December 31, 2023 and 2022, and related information as of December 31, 2023, is as follows: Options Outstanding Number of Weighted Weighted Aggregate Options outstanding – December 31, 2021 904,123 $ 5.59 Granted 60,000 2.31 Exercised — — Forfeited and cancelled (259,163 ) 4.74 Options outstanding – December 31, 2022 704,960 $ 5.62 8.29 $ 18 Granted — — Exercised — — Forfeited and cancelled (88,253 ) 11.68 Options outstanding – December 31, 2023 616,707 $ 4.76 7.35 $ — Options exercisable – December 31, 2023 463,068 $ 5.28 7.29 $ — Options vested and expected to vest – December 31, 2023 616,661 $ 4.76 7.35 $ —
Schedule of RSU Activity		A summary of RSU activity for the year ended December 31, 2023 is presented below: Restricted Stock Units Number of Weighted RSUs outstanding – December 31, 2021 — $ — Granted 91,000 2.21 Vested and released — — Forfeited and cancelled — — RSUs outstanding – December 31, 2022 91,000 $ 2.21 Granted — — Vested and released (91,000 ) 2.21 Forfeited and cancelled — — RSUs outstanding – December 31, 2023 — $ —
Schedule of Non-cash, Share-based Compensation Expense	For the three months ended March 31, 2024 and 2023, ARCA recognized the following non -cash -based Three Months Ended 2024 2023 General and administrative $ 114 $ 163 Research and development — 41 Total $ 114 $ 204	For the years ended December 31, 2023 and 2022, ARCA recognized the following non -cash -based Years Ended 2023 2022 General and administrative $ 526 $ 423 Research and development 160 133 Total $ 686 $ 556

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2023
Income Taxes [Abstract]
Schedule of Income Tax Benefit Attributable to Our Loss from Operations	Income tax benefit attributable to ARCA’s loss from operations before income taxes differs from the amounts computed by applying the U.S. federal statutory income tax rate of 21% for 2023 and 2022, as a result of the following (in thousands): Years ended 2023 2022 U.S. federal income tax benefit at statutory rates $ (1,121 ) $ (2,085 ) State income tax benefit, net of federal benefit (192 ) (357 ) Research and experimentation credits — — Deferred tax asset adjustment 47 2 Other 107 186 Change in valuation allowance 1,159 2,254 Income tax benefit $ — $ —
Schedule of Net deferred tax assets and liabilities	Deferred income taxes reflect the net tax effects of temporary differences between the carrying amounts of assets and liabilities for financial reporting and the amounts used for income tax purposes, as well as operating loss and tax credit carryforwards. The income tax effects of temporary differences and carryforwards that give rise to significant portions of ARCA’s net deferred tax assets and liabilities consisted of the following (in thousands): As of December 31, 2023 2022 Deferred tax assets: Net operating loss carryforwards $ 51,190 $ 50,008 Charitable contribution carryforwards 371 393 Research and experimentation credits 2,420 2,420 Capitalized research and development costs 951 979 Capitalized intangibles 354 356 Stock-based compensation 232 205 Accrued compensation 7 6 Lease liabilities 69 94 Total deferred tax assets 55,594 54,461 Valuation allowance (55,531 ) (54,372 ) Deferred tax assets, net of valuation allowance 63 89 Deferred tax liabilities: Right-of-use asset (61 ) (84 ) Depreciation and amortization (2 ) (5 ) Net deferred tax liability $ — $ —

ARCA and Summary of Significa_2

ARCA and Summary of Significant Accounting Policies (Details)	3 Months Ended	12 Months Ended
	Mar. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)
ARCA and Summary of Significant Accounting Policies [Abstract]
Revenue	$ 0	$ 0
Off-balance-sheet concentrations of credit risk	$ 0	$ 0
Number of segment		1

Net Loss Per Share (Details) -

Net Loss Per Share (Details) - Schedule of Potentially Dilutive Shares of Common Stock - shares	3 Months Ended		12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023	Dec. 31, 2022
Potentially dilutive securities, excluded:
Potentially dilutive securities, excluded	645,845	755,857	616,707	795,960
Outstanding stock options
Potentially dilutive securities, excluded:
Potentially dilutive securities, excluded	645,845	664,857	616,707	704,960
Unvested restricted stock units
Potentially dilutive securities, excluded:
Potentially dilutive securities, excluded		91,000		91,000

Fair Value Disclosures (Details

Fair Value Disclosures (Details) - USD ($) $ in Millions		3 Months Ended	12 Months Ended
	Dec. 31, 2022	Mar. 31, 2024	Dec. 31, 2023
Fair Value Disclosures (Details) [Line Items]
Fair value hierarchy
Debt outstanding
Marketable securities
Money Market Funds | Fair Value Measurements, Recurring | Level 1
Fair Value Disclosures (Details) [Line Items]
Cash equivalents	$ 42.4	$ 35.9	$ 37.4

Property and Equipment (Details

Property and Equipment (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023	Dec. 31, 2022
Property and Equipment [Abstract]
Depreciation and amortization expense	$ 3	$ 4	$ 15	$ 20

Property and Equipment (Detai_2

Property and Equipment (Details) - Schedule of Property and Equipment - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Schedule of Property and Equipment [Line Items]
Property and Equipment, Gross	$ 222	$ 222	$ 229
Accumulated depreciation and amortization	(215)	(212)	(204)
Property and equipment, net	7	10	25
Computer equipment
Schedule of Property and Equipment [Line Items]
Property and Equipment, Gross	$ 39	$ 39	39
Estimated Life	3 years	3 years
Lab equipment
Schedule of Property and Equipment [Line Items]
Property and Equipment, Gross	$ 130	$ 130	130
Estimated Life	5 years	5 years
Furniture and fixtures
Schedule of Property and Equipment [Line Items]
Property and Equipment, Gross	$ 37	$ 37	44
Estimated Life	5 years	5 years
Computer software
Schedule of Property and Equipment [Line Items]
Property and Equipment, Gross	$ 16	$ 16	$ 16
Estimated Life	3 years	3 years

Related Party Arrangements (Det

Related Party Arrangements (Details) - Chief Executive Officer [Member] - USD ($)	1 Months Ended	3 Months Ended		12 Months Ended
	Dec. 31, 2023	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023	Dec. 31, 2022
Related Party Arrangements [Line Items]
Related party expense		$ 0	$ 108,000	$ (91,000)	$ 432,000
Payment of unrestricted research grants	$ 125,000			$ 125,000

Commitments and Contingencies_2

Commitments and Contingencies (Details) € in Millions				1 Months Ended		3 Months Ended		12 Months Ended
	Nov. 30, 2023	Oct. 31, 2023	Aug. 29, 2020 ft²	Jul. 31, 2021 EUR (€)	Jun. 30, 2021 ft²	Mar. 31, 2024 USD ($)	Mar. 31, 2023 USD ($)	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Apr. 30, 2024 USD ($)
Commitments and Contingencies (Details) [Line Items]
Amount of retention bonuses						$ 311,000		$ 311,000
Percentage of retention bonuses	50%
Retention bonus paid								86,000
Severance expense								159,000
Remains unpaid
Workforce reduction percentage									67%
Number of employees									12
Square feet (in Square Feet) | ft²			5,200
Lease term			42 months
Lease renewal option			option to renew for an additional 36 month term at the then prevailing rental rate.			to extend the lease term six (6) months through September 2024
Term			36 months			6 months
Square feet office facilities (in Square Feet) | ft²					3,000
Sublease term		29 months			29 months
Lessee operating lease description						The leases include real estate taxes and insurance, which is not a lease component and is not included in the lease obligation. In addition, common area maintenance charges are based on actual costs incurred and are a non-lease component that is not included in the lease obligation.		The leases include real estate taxes and insurance, which is not a lease component and is not included in the lease obligation. In addition, common area maintenance charges are based on actual costs incurred and are a non-lease component that is not included in the lease obligation.
Lease liability						$ 48,000		$ 280,000
Operating leases						$ 23,000	$ 33,000	$ 127,000	$ 131,000
Weighted-average discount rate						7%		7%
Weighted-average remaining lease term						6 months		3 years 2 months 12 days
Indicates (true false) whether lessee has option to extend operating lease						false
Additional operating lease term						September 2024
Percentage Of Base Rent To Be Paid Monthly						125%
Clinical development decisions
Commitments and Contingencies (Details) [Line Items]
Amount of retention bonuses									265,000
General and Administrative Expense
Commitments and Contingencies (Details) [Line Items]
Rent expense						$ 22,000	$ 31,000	$ 119,000	125,000
One-time Termination Benefits
Commitments and Contingencies (Details) [Line Items]
Restructuring charges									755,000
One-time Termination Benefits | Research and development
Commitments and Contingencies (Details) [Line Items]
Restructuring charges									470,000
One-time Termination Benefits | General and Administrative Expense
Commitments and Contingencies (Details) [Line Items]
Restructuring charges									$ 285,000
Subsequent Event
Commitments and Contingencies (Details) [Line Items]
Amount of retention bonuses										$ 444,000
University Medical Center Of Johannes Gutenberg University Mainz | Research and development | Patent Assignment Agreement
Commitments and Contingencies (Details) [Line Items]
Royalty obligations (in Euro) | €				€ 1.6

Commitments and Contingencies_3

Commitments and Contingencies (Details) - Schedule of Future Minimum Commitments Due - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Schedule of Future Minimum Commitments Due [Abstract]
2024		$ 93
2025		96
2026		100
2027		25
Total remaining lease payments	$ 49	314
Less: imputed lease interest	(1)	(34)
Less: Current portion	(48)	(76)
Operating lease liability, net of current portion		$ 204	$ 280

Equity Financings (Details)

Equity Financings (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2020	Jul. 22, 2020
Equity Financings (Details) [Line Items]
Common stock, par value (in Dollars per share)	$ 0.001		$ 0.001	$ 0.001
2020 Sales Agreement
Equity Financings (Details) [Line Items]
Sale of common stock	0	0	0	0
Jones Trading
Equity Financings (Details) [Line Items]
Percentage of commission rate equal						3%
Jones Trading | Sales Agreement
Equity Financings (Details) [Line Items]
Common stock, par value (in Dollars per share)					$ 0.001	$ 0.001
Aggregate offering price (in Dollars)						$ 54

Share-based Compensation (Detai

Share-based Compensation (Details) - USD ($)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Mar. 31, 2024	Dec. 31, 2021	Dec. 10, 2020
Share-based Compensation (Details) [Line Items]
Purchase options shares	616,707	704,960	645,845	904,123
Weighted average exercise price (in Dollars per share)	$ 4.76	$ 5.62	$ 4.3	$ 5.59
Stock options award, expiration	10 years
Employee Stock Option
Share-based Compensation (Details) [Line Items]
Unrecognized compensation expense (in Dollars)		$ 367,000
Weighted average period	1 year 1 month 6 days
Restricted Stock Units
Share-based Compensation (Details) [Line Items]
Stock awards granted service period	1 year
Unrecognized compensation cost (in Dollars)	$ 0
Minimum
Share-based Compensation (Details) [Line Items]
Stock options award, vesting period	3 years
Exercise price per share	10%
Minimum | Incentive Stock Option
Share-based Compensation (Details) [Line Items]
Percentage of exercise price	100%
Minimum | Incentive Stock Option | Stockholders
Share-based Compensation (Details) [Line Items]
Percentage of exercise price	110%
Maximum
Share-based Compensation (Details) [Line Items]
Stock options award, vesting period	4 years
2020 Equity Incentive Plan
Share-based Compensation (Details) [Line Items]
Number of shares issuable					1,167,425
Purchase options shares	601,900
Weighted average exercise price (in Dollars per share)	$ 3.45
Reserved shares	459,718
Options granted	0
Purchase aggregate shares		60,000
2013 Plan
Share-based Compensation (Details) [Line Items]
Purchase options shares	14,807
Weighted average exercise price (in Dollars per share)	$ 57.73

Share-based Compensation (Det_2

Share-based Compensation (Details) - Schedule of Estimated Weighted Average Grant Date Fair Value Per Share	12 Months Ended
	Dec. 31, 2023 $ / shares
Schedule of Estimated Weighted Average Grant Date Fair Value Per Share [Abstract]
Expected term	5 years 6 months
Expected volatility	107%
Risk-free interest rate	3.56%
Expected dividend yield	0%
Weighted-average grant date fair value per share (in Dollars per share)	$ 1.87

Share-based Compensation (Det_3

Share-based Compensation (Details) - Schedule of Stock Option Activities - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended	12 Months Ended
	Dec. 31, 2023	Mar. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Schedule of Stock Option Activities [Abstract]
Number of Options, Options outstanding, ending balance	616,707	645,845	616,707	704,960
Weighted Average Exercise Price, Options outstanding, ending balance	$ 4.76	$ 4.3	$ 4.76	$ 5.62
Weighted Average Remaining Contractual Term (in years) Options outstanding, ending balance	7 years 4 months 6 days	6 years 9 months 25 days	7 years 4 months 6 days	8 years 3 months 14 days
Aggregate Intrinsic Value, Options outstanding, ending balance				$ 18
Number of Options, Options exercisable, ending balance	463,068	502,517	463,068
Weighted Average Exercise Price, Options exercisable, ending balance	$ 5.28	$ 4.71	$ 5.28
Weighted Average Remaining Contractual Term (in years), Options exercisable, ending balance		6 years 6 months 18 days	7 years 3 months 14 days
Aggregate Intrinsic Value, Options exercisable, ending balance
Number of Options, Options vested and expected to vest, ending balance	616,661	645,816	616,661
Weighted Average Exercise Price, Options vested and expected to vest, ending balance	$ 4.76	$ 4.3	$ 4.76
Weighted Average Remaining Contractual Term (in years), Options vested and expected to vest, ending balance		6 years 9 months 25 days	7 years 4 months 6 days
Aggregate Intrinsic Value, Options vested and expected to vest, ending balance
Number of Options, Granted		42,000		60,000
Weighted Average Exercise Price, Granted		$ 1.64		$ 2.31
Number of Options, Exercised
Weighted Average Exercise Price, Exercised
Number of Options, Forfeited and cancelled		(12,862)	(88,253)	(259,163)
Weighted Average Exercise Price, Forfeited and cancelled		$ 17.45	$ 11.68	$ 4.74

Share-based Compensation (Det_4

Share-based Compensation (Details) - Schedule of RSU Activity - $ / shares	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Schedule of RSU Activity [Abstract]
Number of Shares, RSUs outstanding, beginning of period	91,000
Weighted Average Grant Date Date Fair Value, RSUs outstanding, beginning of period	$ 2.21
Number of Shares, RSUs outstanding, Granted		91,000
Weighted Average Grant Date Date Fair Value, RSUs outstanding, Granted		$ 2.21
Number of Shares, RSUs outstanding, Vested and released	(91,000)
Weighted Average Grant Date Date Fair Value, RSUs outstanding, Vested and released	$ 2.21
Number of Shares, RSUs outstanding, Forfeited and cancelled
Weighted Average Grant Date Date Fair Value, RSUs outstanding, Forfeited and cancelled
Number of Shares, RSUs outstanding, ending balance		91,000
Weighted Average Grant Date Date Fair Value, RSUs outstanding, ending balance		$ 2.21

Share-based Compensation (Det_5

Share-based Compensation (Details) - Schedule of Non-cash, Share-based Compensation Expense - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023	Dec. 31, 2022
Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total expenses	$ 114	$ 204	$ 686	$ 556
General and Administrative
Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total expenses	114	163	526	423
Research and Development
Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total expenses		$ 41	$ 160	$ 133

Employee Benefit Plans (Details

Employee Benefit Plans (Details) - USD ($)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Employee Benefit Plans (Details) [Line Items]
Matching contribution	matching contribution equal to 100% of the employee’s first 3% of the employee’s contributions and 50% of the employee’s next 2% of contributions.
Company's contribution (in Dollars)	$ 56,000	$ 96,000
First 3% of pay contributed
Employee Benefit Plans (Details) [Line Items]
Employee’s contribution percentage	100%
Equal contribution percentage	3%
Next 2% of pay contributed
Employee Benefit Plans (Details) [Line Items]
Employee’s contribution percentage	50%
Equal contribution percentage	2%

Income Taxes (Details)

Income Taxes (Details) - USD ($)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2017	Mar. 31, 2024
Income Taxes (Details) [Line Items]
Net operating loss carryforwards	$ 208,100,000
Operating loss carryforwards, limitations on use	The net operating loss carryforwards beginning in 2018, have no expiration.
Valuation allowance	$ 55,500,000
Increase in net deferred tax assets and liabilities	$ 1,200,000
Federal statutory income tax rate	21%	21%
Open Tax Year	2009
Reserve for uncertain tax positions	$ 0	$ 0
Interest or penalties recognized	0	$ 0
Research Tax Credit Carryforward
Income Taxes (Details) [Line Items]
Research and experimentation credits	$ 2,400,000
Tax credit carryforward, limitations on use	Utilization of net operating losses and tax credits, including those acquired as a result of the Merger, will be subject to an annual limitation due to ownership change limitations provided by Internal Revenue Code Section 382. ARCA believes that an ownership change limitation as defined under Section 382 of the U.S. Internal Revenue Code occurred as a result of its various historical financing transactions. Future utilization of the federal net operating losses and tax credit carryforwards accumulated from June 2005 to the change in ownership date will be subject to annual limitations to offset future taxable income. The annual limitation may result in the expiration of the net operating losses and credits before utilization. As such, a portion of ARCA’s net operating loss carryforwards may be limited.
Earliest Tax Year
Income Taxes (Details) [Line Items]
Operating loss carryforwards expiration year			2025
Latest Tax Year
Income Taxes (Details) [Line Items]
Operating loss carryforwards expiration year			2037

Income Taxes (Details) - Schedu

Income Taxes (Details) - Schedule of Income Tax Benefit Attributable to Our Loss from Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Schedule Of Income Tax Benefit Attributable To Our Loss From Operations Abstract
U.S. federal income tax benefit at statutory rates	$ (1,121)	$ (2,085)
State income tax benefit, net of federal benefit	(192)	(357)
Research and experimentation credits
Deferred tax asset adjustment	47	2
Other	107	186
Change in valuation allowance	1,159	2,254
Income tax benefit

Income Taxes (Details) - Sche_2

Income Taxes (Details) - Schedule of Net deferred tax assets and liabilities - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Deferred tax assets:
Net operating loss carryforwards	$ 51,190	$ 50,008
Charitable contribution carryforwards	371	393
Research and experimentation credits	2,420	2,420
Capitalized research and development costs	951	979
Capitalized intangibles	354	356
Stock-based compensation	232	205
Accrued compensation	7	6
Lease liabilities	69	94
Total deferred tax assets	55,594	54,461
Valuation allowance	(55,531)	(54,372)
Deferred tax assets, net of valuation allowance	63	89
Deferred tax liabilities:
Right-of-use asset	(61)	(84)
Depreciation and amortization	(2)	(5)
Net deferred tax liability

Net Loss Per Share (Details) _2

Net Loss Per Share (Details) - Schedule of Potentially Dilutive Shares of Common Stock - shares	3 Months Ended		12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023	Dec. 31, 2022
Potentially dilutive securities, excluded:
Potentially dilutive securities, excluded	645,845	755,857	616,707	795,960
Outstanding stock options
Potentially dilutive securities, excluded:
Potentially dilutive securities, excluded	645,845	664,857	616,707	704,960
Unvested restricted stock units
Potentially dilutive securities, excluded:
Potentially dilutive securities, excluded		91,000		91,000

Property and Equipment (Detai_3

Property and Equipment (Details) - Schedule of Property and Equipment - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Schedule of Property and Equipment [Line Items]
Property and Equipment, Gross	$ 222	$ 222	$ 229
Accumulated depreciation and amortization	(215)	(212)	(204)
Property and equipment, net	7	10	25
Computer Equipment
Schedule of Property and Equipment [Line Items]
Property and Equipment, Gross	$ 39	$ 39	39
Estimated Life	3 years	3 years
Lab Equipment
Schedule of Property and Equipment [Line Items]
Property and Equipment, Gross	$ 130	$ 130	130
Estimated Life	5 years	5 years
Furniture and Fixtures
Schedule of Property and Equipment [Line Items]
Property and Equipment, Gross	$ 37	$ 37	44
Estimated Life	5 years	5 years
Computer Software
Schedule of Property and Equipment [Line Items]
Property and Equipment, Gross	$ 16	$ 16	$ 16
Estimated Life	3 years	3 years

Commitments and Contingencies_4

Commitments and Contingencies (Details) - Schedule of Future Minimum Commitments Due - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Schedule of Future Minimum Commitments Due [Abstract]
2024	$ 49
Total remaining lease payments	49	$ 314
Less: imputed lease interest	(1)	(34)
Less: Current portion	(48)	(76)
Operating lease liability, net of current portion		$ 204	$ 280

Share-based Compensation (Det_6

Share-based Compensation (Details) - Schedule of Non-cash, Share-based Compensation Expense - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023	Dec. 31, 2022
Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total expenses	$ 114	$ 204	$ 686	$ 556
General and Administrative
Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total expenses	114	163	526	423
Research and Development
Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total expenses		$ 41	$ 160	$ 133

Share-based Compensation (Det_7

Share-based Compensation (Details) - Schedule of Stock Option Activities - $ / shares		3 Months Ended	12 Months Ended
	Dec. 31, 2023	Mar. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Schedule of Stock Option Activities [Abstract]
Number of Options, Options outstanding, ending balance	616,707	645,845	616,707	704,960
Weighted Average Exercise Price, Options outstanding, ending balance	$ 4.76	$ 4.3	$ 4.76	$ 5.62
Weighted Average Remaining Contractual Term (in years) Options outstanding, ending balance	7 years 4 months 6 days	6 years 9 months 25 days	7 years 4 months 6 days	8 years 3 months 14 days
Number of Options, Options exercisable, ending balance	463,068	502,517	463,068
Weighted Average Exercise Price, Options exercisable, ending balance	$ 5.28	$ 4.71	$ 5.28
Weighted Average Remaining Contractual Term (in years), Options exercisable, ending balance		6 years 6 months 18 days	7 years 3 months 14 days
Number of Options, Options vested and expected to vest, ending balance	616,661	645,816	616,661
Weighted Average Exercise Price, Options vested and expected to vest, ending balance	$ 4.76	$ 4.3	$ 4.76
Weighted Average Remaining Contractual Term (in years), Options vested and expected to vest, ending balance		6 years 9 months 25 days	7 years 4 months 6 days
Number of Options, Granted		42,000		60,000
Weighted Average Exercise Price, Granted		$ 1.64		$ 2.31
Number of Options, Exercised
Weighted Average Exercise Price, Exercised
Number of Options, Forfeited and cancelled		(12,862)	(88,253)	(259,163)
Weighted Average Exercise Price, Forfeited and cancelled		$ 17.45	$ 11.68	$ 4.74

Subsequent Events (Details)

Subsequent Events (Details) - Subsequent Event [Member] - USD ($)	Apr. 20, 2024	Apr. 03, 2024	Apr. 30, 2024
Subsequent Events (Details) [Line Items]
Declared cash dividend		$ 5,000,000
Retention bonuses			$ 444,000
ARCA and Oruka
Subsequent Events (Details) [Line Items]
Percentage of ownership interest		97.62%
ARCA
Subsequent Events (Details) [Line Items]
Number of consecutive trading days		5 days
Adjusted exchange ratio		$ 5,000,000
ARCA | ARCA and Oruka
Subsequent Events (Details) [Line Items]
Percentage of noncontrolling ownership interest		2.38%
Common Stock | ARCA
Subsequent Events (Details) [Line Items]
Initially specified percentage for beneficial number of shares		9.99%
Common Stock and Pre Funded Warrants [Member] | Oruka Therapeutics Inc
Subsequent Events (Details) [Line Items]
Aggregate purchase price		$ 275,000,000
Merger Agreement | ARCA and Oruka
Subsequent Events (Details) [Line Items]
Payment of other party termination fee		440,000
Merger Agreement | Minimum [Member]
Subsequent Events (Details) [Line Items]
Subscription agreement receipt amount		$ 175,000,000
First Merger | Oruka Therapeutics Inc
Subsequent Events (Details) [Line Items]
Excepted number of board members		5
Seperation Agreement
Subsequent Events (Details) [Line Items]
Number of months base salary		12 months
Cash payment		$ 25,000
Thomas A. Keuer | Second Amendment of Certain Retention Bonus Letters
Subsequent Events (Details) [Line Items]
Increase of retention bonus to each executive	$ 200,000
C. Jeffrey Dekker | Second Amendment of Certain Retention Bonus Letters
Subsequent Events (Details) [Line Items]
Increase of retention bonus to each executive	200,000
Thomas A. Keuer and C. Jeffrey Dekker [Member]
Subsequent Events (Details) [Line Items]
Retention bonuses	$ 165,000
Series B Preferred Stock
Subsequent Events (Details) [Line Items]
Minimum percentage of originally issued outstanding		30%
Minimum percentage of originally issued outstanding		30%
Series B Preferred Stock | Merger Agreement
Subsequent Events (Details) [Line Items]
Preferred stock, par value (in Dollars per share)		$ 0.001
Series B Preferred Stock | First Merger | Common Stock | ARCA
Subsequent Events (Details) [Line Items]
Preferred stock convertible shares issuable (in Shares)		1,000