FIRST AMENDMENT TO SUBLEASE

This First Amendment to Sublease is dated as of July 15, 1998 by and between
SatCon Technology Corporation, a Delaware corporation having a place of business
at 161 First Street, Cambridge, Massachusetts 02142 ("Sublandlord") and EPIX
Medical, Inc., a Delaware corp. having a place of business at 161 First Street,
Cambridge, Massachusetts 02142 ("Subtenant").

                                   BACKGROUND

A. Sublandlord and Subtenant are parties to a certain Sublease dated as of
October 31, 1997 (the "Sublease") with respect to certain premises located at
161 First Street, Cambridge, Massachusetts (the "Premises").

B. Sublandlord and Subtenant desire to amend the Sublease to, among other
matters, extend the term thereof and to add additional space to the Premises.

                                    AGREEMENT

In consideration of the foregoing, and for other good and valuable
consideration, Sublandlord and Subtenant hereby agree as follows:

1. Capitalized terms used herein and not defined herein shall have the meaning
given to them in the Sublease.

2. Effective as of July 15, 1998: (i) the Premises shall mean the Premises
demised under the Sublease (the "Third Floor Premises") as well as 3,952
rentable square feet of space located on the first floor of the Building and
shown on Exhibit A attached hereto (the "First Floor Premises") and (ii) the
Monthly Fixed Rent shall be $23,617.00.

3. Effective as of July 15, 1998, all references in Sections 3.2 and 5.1 to
"19.49%" shall be deleted and the words "Subtenant's Proportionate Share" shall
be inserted in lieu thereof. Effective as of July 15, 1998, Subtenant's
Proportionate Share shall mean 28.11%.

4. Sublandlord has entered into an amendment to the Overlease, a copy of which
is attached hereto as Exhibit B. All references in the Sublease to the Overlease
shall mean the Overlease as so amended.

5. Notwithstanding the provisions of Section 2.2 of the Overlease, the Term
shall be extended from November 1, 1998 through December 31, 1999 (the "First
Extension Term"). All of the terms and conditions of the Sublease shall continue
in full force

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and effect during the First Extension Term, except that (i) the Monthly Fixed
Rent with respect to the Third Floor Premises shall be $20,860.54, (ii) the
rentable area of the Third Floor Premises shall be 9,358 (to correct an error in
the calculation thereof set forth in the Sublease) and the Monthly Fixed Rent
with respect to the First Floor Premises shall be $5,928.00, (iii) the
Subtenant's Proportionate Share shall be 29.05%, and (iv) the second sentence of
Section 3.2 of the Sublease is amended in its entirety to read as follows:
"Subtenant shall pay Sublandlord, as Additional Rent, Subtenant's Proportionate
Share of Expense Pass Throughs allocable to periods of time included in the
First Extension Term and on a basis that accounts for allocation based on the
provision of services between Sublandlord and Subtenant such that each party
pays for services consistent with receipt and disproportionate services are
allocated accordingly." In addition, provided Subtenant shall not be in default
of its obligations hereunder beyond applicable grace or cure periods, Subtenant
shall have the right to extend the Term of the Sublease for an additional period
of one, two or three years by notice given to Sublandlord on or before July 1,
1999, time being of the essence (the "Second Extension Term"). Subtenant's
notice to Sublandlord exercising its right to extend the Term shall specify the
period of such extension and failure to specify such a period shall be deemed a
failure to have exercised such extension right. All of the terms and conditions
of the Sublease shall remain in full force and effect during the Second
Extension Term, except that Subtenant shall have no further extension options
and notwithstanding the provisions of Section 2.1 of the Sublease, the rate for
parking in Sublandlord's Rogers Street Parking Lot shall be $100 per month
through October 31, 2000, and thereafter shall be at the rate payable by
Sublandlord under its lease for such spaces.

6. In the event Subtenant fails to exercise its option for the Second Extension
Term in the manner set forth in Section 5 above, Subtenant shall pay Sublandlord
a termination fee of $50,000 on or before December 1, 1999.

7. Section 8.8 of the Sublease is amended by adding the following sentence to
the end of the existing provisions: "Subject to receipt of Overlandlord's
consent, Subtenant shall be permitted to install an exterior sign on the left
side of the front entrance to the Building which is symmetrical and to and
similar in design to the Sublandlord's sign which is located on the right side
of the front entrance to the Building."

8. Subtenant shall bear one half of the legal fees and costs incurred by
Sublandlord in connection with the preparation of this First Amendment to
Sublease, Subtenant's share of which shall not exceed $2500.

9. Sublandlord warrants and represents to Subtenant and Subtenant represents and
warrants to Sublandlord that neither party has dealt with any broker or other
person (including, without limitation, with respect to Subtenant, McCall and
Almy) entitled to a broker's commission or finder's fee in connection with the
negotiation or

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execution of this Agreement or the consummation of the transaction contemplated
hereby, and Sublandlord and Subtenant each agree to, at its own sole cost and
expense, defend the other and hold the other harmless and indemnify the other
from and against all damages, claims, losses and liabilities, including legal
fees, incurred by the other, arising out of or resulting from the breach of its
representation and warranty.

10. Sublandlord and Subtenant hereby acknowledge and agree that this Sublease
shall be deemed terminated and of no further force or effect unless Landlord
shall have consented to this Sublease (such consent to be reasonably acceptable
to both Sublandlord and Subtenant) on or before August 14, 1998.

11. Sublandlord represents and warrants that: (i) the Overlease has not been
modified, amended or terminated except as set forth herein and is in full force
and effect; (ii) Sublandlord is not in default of any of its obligations under
the Overlease nor has Sublandlord done or failed to do anything which with
notice, the passage of time, or both, could ripen into a default under the
Overlease; (iii) to the best of Sublandlord's knowledge, Overlandlord is not in
default under any of its obligations under the Overlease nor, to the best of
Sublandlord's knowledge, has Overlandlord done or failed to do anything which
with notice, the passage of time, or both, could ripen into a default under the
Overlease.

12. Except as amended hereby, the Sublease is in all other respect ratified and
confirmed.

         EXECUTED as a sealed instrument in two or more counterparts on the day
and year first above written.

         Sublandlord:

         SatCon Technology Corporation

         By: /s/  M.C. Turmelle
                  ------------------------
                  Title: VP, CFO

         Subtenant:

         EPIX Medical, Inc.

         By: /s/ M.D. Webb
                 -------------------------
                 Title: CEO


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