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                                                                    EXHIBIT 3.6

                            CERTIFICATE OF AMENDMENT

                                       OF

                  THE RESTATED CERTIFICATE OF INCORPORATION OF

                          CARDIOTHORACIC SYSTEMS, INC.

         CardioThoracic Systems, Inc., a corporation organized and existing
under and by virtue of the General Corporation Law of the State of Delaware,

DOES HEREBY CERTIFY:

FIRST: The name of this corporation is CardioThoracic Systems, Inc. This
corporation was originally incorporated under the same name, and the original
Certificate of Incorporation was filed with the Secretary of State of the State
of Delaware on February 20, 1996.

SECOND: That at a meeting of the Board of Directors of CardioThoracic Systems,
Inc., resolutions were duly adopted setting forth proposed amendments of the
Restated Certificate of Incorporation of said corporation, declaring said
amendments to be advisable and calling for the submission thereof to the
stockholders of said corporation for adoption. The resolutions setting forth the
proposed amendments are as follows:

         RESOLVED: That the first paragraph of Article IV of the Restated
         Certificate of Incorporation of this corporation be amended and
         restated to read in its entirety as follows:

                           The Corporation is authorized to issue two classes of
                  shares of stock to be designated, respectively, Common Stock,
                  $0.001 par value, and Preferred Stock, $0.001 par value. The
                  total number of shares that the Corporation is authorized to
                  issue is 65,100,000 shares. The number of shares of Common
                  Stock authorized is 60,000,000. The number of shares of
                  Preferred authorized is 5,100,000.

         RESOLVED FURTHER: That Article X of the Restated Certificate of
         Incorporation of this corporation be amended and restated to read in
         its entirety as follows:

                           1. Number of Directors. The number of directors which
                  constitutes the whole Board of Directors of the corporation
                  shall be designated in the Bylaws of the corporation. The
                  directors shall be divided into three classes with the term of
                  office of the first class (Class I) to expire at the annual
                  meeting of stockholders held in 1998; the term of office of
                  the second class (Class II) to expire at the annual meeting of
                  stockholders held in 1999; the term of office of the third


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                  class (Class III) to expire at the annual meeting of
                  stockholders held in 2000; and thereafter for each such term
                  to expire at each third succeeding annual meeting of
                  stockholders after such election.

                           2. Election of Directors. Elections of directors need
                  not be by written ballot unless the Bylaws of the corporation
                  shall so provide.

THIRD: That thereafter, pursuant to resolution of its Board of Directors, the
approval of the stockholders of said corporation was duly obtained in accordance
with Section 242 of the General Corporation Law of the state of Delaware at
which time the necessary number of shares as required by statute were voted in
favor of the amendment.

FOURTH: That said amendment was duly adopted in accordance with the provisions
of Section 242 of the General Corporation Law of the State of Delaware.

         IN WITNESS WHEREOF, CardioThoracic Systems, Inc. has caused this
certificate to be signed by Richard M. Ferrari, its President, and J. Casey
McGlynn, its Secretary, this 27th day of May, 1997.

                                            BY: /s/ RICHARD M. FERRARI
                                                --------------------------------
                                                Richard M. Ferrari, President

ATTEST: /s/ J. CASEY MCGLYNN
        ---------------------------------
       J. Casey McGlynn, Secretary