EXHIBIT 5.1

                              September 29, 1997



ABIOMED, Inc.
33 Cherry Hill Drive
Danvers, MA 01923

     RE:  Registration Statement on Form S-3 of ABIOMED, Inc.
          filed on September 29, 1997
          -------------------------------------------------------

Ladies and Gentlemen:

     We have acted as counsel to ABIOMED, Inc., a Delaware corporation (the
"Company"), in connection with the preparation and filing with the Securities
and Exchange Commission of a Registration Statement on Form S-3 (the
"Registration Statement") pursuant to which the Company is registering under the
Securities Act of 1933, as amended (the "Act"), a total of 2,760,000 shares of
common stock, $.01 par value (the "Common Stock") and 2,760,000 Rights, as
defined below.  Pursuant to the Registration Statement and an underwriting
agreement (the "Underwriting Agreement") by and among the Company, Robertson,
Stephens & Company and UBS Securities, as representatives of the several
underwriters (the "Underwriters") and certain of the Company's Stockholders (the
"Selling Stockholders"), in substantially the form to be filed as Exhibit 1.01
to the Registration Statement, the Company proposes to sell to the Underwriters
up to 2,610,000 shares of Common Stock (the "Company Shares") and the Selling
Stockholders propose to sell to the Underwriters 150,000 shares of Common Stock
(the "Selling Stockholder Shares"). The Rights are issuable pursuant to that
certain Rights Agreement, dated as of August 13, 1997 (the "Rights Agreement"),
providing, in effect, for the delivery of a right (a "Right"), along with each
share of Common Stock issued by the Company pursuant to the Underwriting
Agreement. This opinion is being rendered in connection with the filing of the
Registration Statement. Unless otherwise indicated, capitalized terms used
herein shall have the meanings ascribed thereto in the Underwriting Agreement.
 
     For purposes of this opinion, we have assumed, without any investigation,
(i) the legal capacity of each natural person, (ii) the full power and authority
of each entity and person other than the Company to execute, deliver and perform
each document heretofore executed and delivered or hereafter to be executed and
delivered and to do each other act heretofore done or hereafter to be done by
such entity or person, (iii) the due authorization by each entity or person
other than the Company of each document heretofore executed and delivered or
hereafter to be executed and delivered and to do each other act heretofore done
or to be done by such entity or person, (iv) the due execution and delivery by
each entity or person other than the Company of

 
ABIOMED, Inc.
September 29, 1997
Page 2


each document heretofore executed and delivered or hereafter to be executed and
delivered by such entity or person, (v) the legality, validity, binding effect
and enforceability as to each entity or person other than the Company of each
document heretofore executed and delivered or hereafter to be executed and
delivered and of each other act heretofore done or hereafter to be done by such
entity or person, (vi) the genuineness of each signature on, and the
completeness of each document submitted to us as an original, (vii) the
conformity to the original of each document submitted to us as a copy, (viii)
the authenticity of the original of each document submitted to us as a copy,
(ix) the completeness, accuracy and proper indexing of all governmental and
judicial records searched and (x) no modification of any provision of any
document, no waiver of any right or remedy and no exercise of any right or
remedy other than in a commercially reasonable and conscionable manner and in
good faith.
 
     In connection with this opinion, we have examined the following
(collectively, the "Documents"):
 
     (i)   the Restated Certificate of Incorporation of the Company filed as
           Exhibit 3.1 to the Registration Statement;

     (ii)  the Restated Bylaws of the Company incorporated by reference as
           Exhibit 3.2 to the Registration Statement;

     (iii) the corporate minute books or other records of the Company;

     (iv)  a specimen certificate for the Common Stock incorporated by reference
           as Exhibit 4.1 to the Registration Statement;

     (v)   the Rights Agreement incorporated by reference as Exhibit 4.03 to the
           Registration Statement; and

     (vi)  the Form of Underwriting Agreement to be filed by amendment as
           Exhibit 1.1 to the Registration Statement.

     The opinions expressed herein are based solely upon (i) our review of the
Documents, (ii) discussions with David M. Lederman, the Chairman of the Board,
Chief Executive Officer and President and Assistant Secretary of the Company and
John F. Thero, the Company's Vice President-Finance, Treasurer and Assistant
Secretary and Chief Financial Officer; (iii) the representations and warranties
of the Company and the Selling Stockholders contained in the Underwriting
Agreement and the exhibits thereto, (iv) discussions with those of our attorneys
who have devoted substantive attention to the matters contained herein, and (v)
such review of published sources of law as we have deemed necessary.
 
     Our opinions contained herein are limited to the laws of The Commonwealth
of Massachusetts, the general corporate laws of the State of Delaware and the
federal law of the United States of America.
 

 
ABIOMED, Inc.
September 29, 1997
Page 3


     Based upon and subject to the foregoing, we are of the opinion that:
 
     1.  The Company Shares to be sold by the Company under the circumstances
contemplated in the Registration Statement are duly authorized and, when
delivered pursuant to the Underwriting Agreement, will be validly issued, fully
paid and nonassessable.

     2.  The Selling Stockholder Shares to be sold by the Selling Stockholders
under the circumstances contemplated in the Registration Statement are duly
authorized, validly issued, fully paid and nonassessable.

     3.  The Rights have been duly authorized and, when issued in accordance
with the terms of the Rights Agreement, will be validly issued, fully paid and
nonassessable.
 
     We understand that this opinion is to be used in connection with the
Registration Statement.  We consent to the filing of this opinion as an Exhibit
to said Registration Statement and to the reference to our firm wherever it
appears in the Registration Statement, including the prospectuses constituting a
part thereof and any amendments thereto.  This opinion may be used in connection
with the offering of the Shares only while the Registration Statement, as it may
be amended from time to time, remains in effect.
 
                               Very truly yours,
 
                               BROWN, RUDNICK, FREED & GESMER
                               By:  BROWN, RUDNICK, FREED & GESMER, P.C.
 
 
                               By:  /s/ Philip J. Flink
                                    ------------------------------------------
                                    Philip J. Flink, A Member
                                    Duly Authorized