Exhibit 5.1

October 25, 2019
AtriCure, Inc.
7555 Innovation Way
Mason, Ohio 45040
| Re: | Registration Statement on FormS-3 |
Ladies and Gentlemen:
We have acted as counsel to AtriCure, Inc., a Delaware corporation (the “Company”), in connection with the registration by the Company of 7,719,907 shares (the “Shares”) of the Company’s common stock, par value $0.001 per share, issued to certain selling stockholders referred to in the prospectus supplement dated October 25, 2019 (the “Prospectus Supplement”), pursuant to the Agreement and Plan of Merger, dated as of August 11, 2019 (the “Merger Agreement”), by and among the Company, SentreHEART, Inc., a Delaware corporation, Stetson Merger Sub, Inc., a Delaware corporation and a wholly-owned subsidiary of AtriCure, Second Stetson Merger Sub, LLC, a Delaware limited liability company and wholly-owned subsidiary of AtriCure, and Shareholder Representative Services LLC, solely in its capacity as Securityholder Representative. The Shares have been registered pursuant to a Registration Statementon Form S-3 (File No. 333-230001) (the “Registration Statement”) filed by the Company with the Securities and Exchange Commission on March 1, 2019.
This opinion letter is being delivered in accordance with the requirements of Item 601(b)(5) ofRegulation S-K under the Securities Act of 1933, as amended (the “Act”).
We have examined the Registration Statement, the Prospectus Supplement, the Merger Agreement, the Second Amended and Restated Certificate of Incorporation of the Company filed with the Secretary of State of the State of Delaware, the Fourth Amended and Restated Bylaws of the Company, and the resolutions adopted by the board of directors of the Company relating to the Registration Statement, the Prospectus Supplement and the issuance of the Shares by the Company. We have also examined originals, or copies of originals certified to our satisfaction, of such agreements, documents, certificates and statements of the Company and other corporate documents and instruments, and have examined such questions of law, as we have considered relevant and necessary as a basis for this opinion letter. We have assumed the authenticity of all documents submitted to us as originals, the genuineness of all signatures, the legal capacity of all persons and the conformity with the original documents of any copies thereof submitted to us for examination. As to facts relevant to the opinions expressed herein, we have relied without independent investigation or verification upon, and assumed the accuracy and completeness of, certificates, letters and oral and written statements and representations of public officials and officers and other representatives of the Company.
