<Page>
Exhibit 10.19
MARCH 22, 2004
FIRST AMENDMENT TO LEASE AGREEMENT
This First Amendment to Lease Agreement ("First Amendment") is made and
entered into this 22nd day of March, 2004 by and between WILLIAM J. CALLAHAN,
an individual with an address c/o P.O. Box 269, Bedford, MA 01730 (the
"Landlord"), and NITROMED, INC., a Delaware corporation having an address at
12 Oak Park Drive, Bedford, MA (the "Tenant").
W I T N E S S E T H
WHEREAS, Landlord and Tenant entered into that certain Lease dated as of
May 29, 1997 (the "Original Lease"); and
WHEREAS, Landlord and Tenant mutually desire to amend the Original Lease
as hereinafter set forth; and
WHEREAS, the Original Lease, as amended by this First Amendment shall be
collectively referred to herein as the "Lease".
NOW, THEREFORE, in consideration of $10.00 and other good and valuable
consideration and in consideration of the covenants and agreements set forth
herein, Landlord and Tenant agree to amend the Original Lease as follows:
1. RECITALS; CAPITALIZED TERMS. The recitals set forth above are true
and correct. Capitalized terms not defined herein will have the definitions
ascribed to them in the Original Lease.
2. TERM. The Term shall be extended for an additional four (4) months
from the current expiration date of May 31, 2004, such that said Term shall
expire at midnight on September 30, 2004. The period from June 1, 2004 until
midnight on September 30, 2004 shall be referred to herein as the "Extended
Term." The Extended Term described in this Section 2 shall not be deemed an
exercise of any rights that Tenant may have had in connection with Section 24
(Extension of Term) of the Original Lease.
3. BASIC RENT. During the Extended Term, Tenant shall pay Basic Rent to
the Landlord at a rate that is equal to one hundred and fifty percent (150%)
of the monthly Basic Rent that is due and payable under Section 6 (Basic
Rent; Additional Rent) of the Original Lease as of the date hereof. The
parties hereby acknowledge and agree that the amount of Basic Rent for each
month of the Extended Term shall be Seventy Two Thousand Five Hundred Dollars
and No/100 ($72,500.00), which amount shall be due on the first day of each
month in advance.
4. LANDLORD'S AND TENANT'S WARRANTIES. Landlord warrants that (i)
Landlord owns the Building; (ii) Landlord has the authority to enter into
this First Amendment with Tenant and that Landlord has performed all acts and
obtained all approvals necessary to make this First Amendment a valid,
binding, legal obligation of Landlord; and (iii) there are no liens or
similar claims (excluding mortgages) upon Landlord or against the Premises.
-1-
<Page>
Tenant warrants that it has the authority to enter into this First
Amendment and that Tenant has performed all acts and obtained all approvals
necessary to make this First Amendment a valid, binding, legal obligation of
Tenant.
5. BROKERS. Landlord and Tenant each represent and warrant to the other
that they have dealt with no broker or agent in connection with this First
Amendment. Landlord and Tenant each agree to indemnify and hold the other
harmless from and against any and all costs, expenses, and liabilities
(including reasonable attorneys' fees) that the other may incur as a result
of a claim by any broker or agent alleging to have acted on behalf of the
indemnifying party in connection with this First Amendment.
6. MISCELLANEOUS. Except as expressly modified hereby, the Original
Lease remains unmodified and in full force and effect. In the event of a
conflict between the terms of the Original Lease and this First Amendment,
the terms of this First Amendment shall control.
7. COUNTERPARTS; FACSIMILE. This Fist Amendment may be executed in
multiple counterparts, each of which together shall form one and the same
original instrument. A facsimile signature on any counterpart shall for all
purposes be deemed to be an original.
IN WITNESS WHEREOF, Landlord and Tenant have executed this First
Amendment to Lease under seal as of the date first written above.
LANDLORD: TENANT:
NITROMED, INC., a Delaware corporation
By: /s/ William J. Callahan By: /s/ Joseph Grimm
------------------------------- -----------------------------------
William J. Callahan, individually Name: Joseph Grimm
Title: CFO/Treasurer
-2-