SECURITIES AND EXCHANGE COMMISSION
                              WASHINGTON, DC 20549

                                   -----------

                                  SCHEDULE 13D
                                 (Rule 13d-101)

             INFORMATION TO BE INCLUDED IN STATEMENTS FILED PURSUANT
             TO RULE 13d-l(a) AND AMENDMENTS THERETO FILED PURSUANT
                                TO RULE 13d-2(a)

                                (Amendment No. 6)

                              Thoratec Corporation
-------------------------------------------------------------------------------
                                (Name of Issuer)

                      Common Stock, no par value per share
-------------------------------------------------------------------------------
                         (Title of Class of Securities)

                                   885175 30 7
------------------------------------------------------------------------------- 
                                 (CUSIP Number)

                             Seth H. Hoogasian, Esq.
                                 General Counsel
                           Thermo Electron Corporation
                                 81 Wyman Street
                        Waltham, Massachusetts 02454-9046
                                 (781) 622-1000
                                                                   
                  (Name, Address and Telephone Number of Person
                Authorized to Receive Notices and Communications)

                                 March 16, 2005
------------------------------------------------------------------------------- 
             (Date of Event Which Requires Filing of This Statement)

     If the filing  person has  previously  filed a statement on Schedule 13G to
report the  acquisition  that is the subject of this Schedule 13D, and is filing
this  schedule  because  of Rule  13d-1(e),  13d-1(f)  or  13d-1(g),  check  the
following box ?.

     Note.  Schedules  filed in paper format shall include a signed original and
five copies of the schedule, including all exhibits. See Rule 13d-7(b) for other
parties to whom copies are to be sent. 

                         (Continued on following pages)





                                                                              

----------------------------------------                                       -------------------------------------
CUSIP NO. 885175 30 7                           13D                                     Page 2 of 4 Pages
----------------------------------------                                       -------------------------------------
-------- -----------------------------------------------------------------------------------------------------------
1. NAMES OF REPORTING PERSONS
         I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS (ENTITIES ONLY)

         Thermo Electron Corporation
         04-2209186
-------- -----------------------------------------------------------------------------------------------------------
2.       CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*                                                   (a) [  ]
                                                                                                             (b) [  ]
-------- -----------------------------------------------------------------------------------------------------------
3. SEC USE ONLY


-------- -----------------------------------------------------------------------------------------------------------
4. SOURCE OF FUNDS*

         SC
-------- -----------------------------------------------------------------------------------------------------------
5.       CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) or 2(e)                  [  ]

-------- -----------------------------------------------------------------------------------------------------------
6. CITIZENSHIP OR PLACE OF ORGANIZATION
         State of Delaware
---------------------------- -------- ------------------------------------------------------------------------------

     NUMBER OF SHARES        7.       SOLE VOTING POWER
BENEFICIALLY OWNED BY EACH                   1,703,765
   REPORTING PERSON WITH
                             -------- ------------------------------------------------------------------------------
                             
                             8.       SHARED VOTING POWER 2,731,779
                             
                             -------- ------------------------------------------------------------------------------

                             9. SOLE DISPOSITIVE POWER
                                             4,435,544
                             -------- ------------------------------------------------------------------------------

                             10. SHARED DISPOSITIVE POWER
                                             -0-
---------------------------- -------- ------------------------------------------------------------------------------

11. AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
           4,435,544

---------- ---------------------------------------------------------------------------------------------------------

12.        CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES*                               [  ] 

---------- ---------------------------------------------------------------------------------------------------------

13.        PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11) 9.2%

---------- ---------------------------------------------------------------------------------------------------------

14. TYPE OF REPORTING PERSON*

           CO
---------- ---------------------------------------------------------------------------------------------------------
                                         *SEE INSTRUCTIONS BEFORE FILLING OUT!





                                                            

       Thermo Electron Corporation, a Delaware corporation ("the "Reporting
Person"), hereby amends its statement on Schedule 13D relating to the common
stock, no par value per share (the "Common Stock"), of Thoratec Corporation
(formerly known as Thoratec Laboratories Corporation), a California corporation
(the "Company").

ITEM 2.         Identity and Background.

       Item 2 is hereby amended and restated as follows:

       This Amendment is being filed by the Reporting Person pursuant to Rule
13d-2 to reflect the change of information previously reported under Item 5 of
its Schedule 13D, as amended.

       The principal business address and principal office address of the
Reporting Person is 81 Wyman Street, Waltham, Massachusetts 02454-9046.

       The Reporting Person is a leading provider of analytical and monitoring
instruments used in a broad range of applications, from life sciences research
to telecommunications to food, drug, and beverage production.

       Appendix A attached to hereto sets forth with respect to each executive
officer and director of the reporting Person the following information:

     (a)  name;
     (b)  business address;
     (c)  present  principal  occupation or employment  and the name,  principal
          business and address of any corporation or other organization in which
          such employment is conducted; and
     (d)  citizenship.

     To the  knowledge of the  Reporting  Person,  there is no person who may be
deemed to be a controlling person of the Reporting Person.

     During the last five  years,  neither  the  Reporting  Person  nor,  to the
knowledge of the  Reporting  Person,  any  executive  officer or director of the
Reporting Person has been convicted in a criminal proceeding  (excluding traffic
violations or similar misdemeanors).

     During the last five  years,  neither  the  Reporting  Person  nor,  to the
knowledge of the  Reporting  Person,  any  executive  officer or director of the
Reporting  Person  has  been a party  to a civil  proceeding  of a  judicial  or
administrative  body of  competent  jurisdiction  which  resulted in a judgment,
decree  or final  order  enjoining  future  violations  of,  or  prohibiting  or
mandating activities subject to, Federal or State securities laws or finding any
violation with respect to such laws.

ITEM 5. Interest in Securities of the Issuer.

     Item 5 is hereby amended as follows:

                                 (Page 3 of 4)



     This  Amendment  is being filed by the  Reporting  Person  pursuant to Rule
13d-2 to reflect  an  increase  in the  percentage  of Common  Stock held by the
Reporting Person as a result of the Company's  repurchase of Common Stock, which
resulted in a net reduction of the total issued and outstanding shares of Common
Stock as reported on the  Company's  Form 10-K for the fiscal year ended January
1, 2005.

                                    SIGNATURE

     After  reasonable  inquiry and to the best of my  knowledge  and belief,  I
certify that the information  set forth in this statement is true,  complete and
correct.


                                Dated:  March 24, 2005

                                THERMO ELECTRON CORPORATION


                                By:  /s/ Kenneth J. Apicerno
                                    ------------------------------------------
                                Name:   Kenneth J. Apicerno
                                Title:  Treasurer
                                 


                                 (Page 4 of 4)



                                                             

                                   APPENDIX A

Thermo Electron Corporation
     The  name,  present  principal  occupation  or  employment  and  beneficial
ownership of shares of common stock of Thoratec  Corporation  (the "Company") of
each  director and executive  officer of Thermo  Electron  Corporation  ("Thermo
Electron") is set forth below.  Unless otherwise noted, all such individuals are
citizens of the United States.  Unless  otherwise noted, the business address of
each  executive  officer  and  director of Thermo  Electron is 81 Wyman  Street,
Waltham, Massachusetts 02454-9046.

Directors


                                                                                                        
-------------------------------------- ---------------------------------------- ---------------------------------------------
                                                                                   Beneficial Ownership of Shares of the
                                                                                            Company Common Stock
                                                                                ------------- ----------------- -------------
                                                                                                   Shares
                                                                                                 Underlying
                                                                                                  Options
                                                                                                Exercisable        Total
       Name/Present Principal                                                   Shares Held    Prior to March    Beneficial
      Occupation or Employment                    Business Address                Outright        16, 2005       Ownership
-------------------------------------- ---------------------------------------- ------------- ----------------- -------------
John L. LaMattina                      Pfizer Inc.                                       0                 0             0
Senior Vice President of Pfizer Inc.   50 Pequot Avenue
and the President of Pfizer Global     New London, Connecticut 06230
Research and Development
-------------------------------------- ---------------------------------------- ------------- ----------------- -------------
Peter J. Manning
Director of Safety Insurance Group                                                       0                 0             0
Inc.
-------------------------------------- ---------------------------------------- ------------- ----------------- -------------
Jim P. Manzi
Chairman of the Board of Thermo
Electron and Chairman of Stonegate                                                       0                 0             0
Capital
-------------------------------------- ---------------------------------------- ------------- ----------------- -------------
Robert A. McCabe                                                                     4,393                 0         4,393
Chairman of Pilot Capital Corporation
-------------------------------------- ---------------------------------------- ------------- ----------------- -------------
Robert W. O'Leary                      Valeant Pharmaceuticals International             0                 0             0
Chairman and Chief Executive Officer   3300 Hyland Avenue
of Valeant Pharmaceuticals             Costa Mesa, California 92626
International
-------------------------------------- ---------------------------------------- ------------- ----------------- -------------
Michael E. Porter                      Harvard Business School                           0                 0             0
Bishop William Lawrence                Soldiers Field Road
University Professor at                Boston, Massachusetts 02163
Harvard Business School
-------------------------------------- ---------------------------------------- ------------- ----------------- -------------
Elaine S. Ullian                       Boston Medical Center                             0                 0             0
President and Chief Executive          Talbot 1
Officer of Boston Medical Center       One Boston Medical Center Place
                                       Boston, Massachusetts 02118
-------------------------------------- ---------------------------------------- ------------- ----------------- -------------
Marijn E. Dekkers(1)                                                                     0                 0             0
President, Chief Executive Officer
and Director of Thermo Electron
-------------------------------------- ---------------------------------------- ------------- ----------------- -------------


(1) Mr. Dekkers is a citizen of The Netherlands.

                                  (Page I - 1


Executive Officers Who are Not Directors

         No person is a controlling stockholder of Thermo Electron.


                                                                                                        
-------------------------------------- ---------------------------------------- ---------------------------------------------
                                                                                   Beneficial Ownership of Shares of the
                                                                                            Company Common Stock
                                                                                ---------------------------------------------
                                                                                                 Shares          
                                                                                                 Underlying
                                                                                                  Options
                                                                                                Exercisable       Total
      Name/Present Principal                     Business Address               Shares Held    Prior to March    Beneficial
      Occupation or Employment                                                    Outright        16, 2005       Ownership
-------------------------------------- ---------------------------------------- ------------- ----------------- -------------
Guy Broadbent(2)                                                                         0                 0             0
Vice President of Thermo Electron
-------------------------------------- ---------------------------------------- ------------- ----------------- -------------
Marc N. Casper                                                                           0                 0             0
Senior Vice President of
Thermo Electron
-------------------------------------- ---------------------------------------- ------------- ----------------- -------------
Seth H. Hoogasian                                                                        0                 0             0
Vice President, General Counsel and
Secretary of Thermo Electron
-------------------------------------- ---------------------------------------- ------------- ----------------- -------------
Peter E. Hornstra                                                                        0                 0             0
Corporate Controller and Chief
Accounting Officer of Thermo Electron
-------------------------------------- ---------------------------------------- ------------- ----------------- -------------
Stephen G. Sheehan                                                                       0                 0             0
Vice President, Human Resources of
Thermo Electron
-------------------------------------- ---------------------------------------- ------------- ----------------- -------------
Peter M. Wilver                                                                          0                 0             0
Vice President and Chief
Financial Officer of Thermo Electron
------------------------------------------------------------------------------- ------------- ----------------- -------------
All directors and current executive officers as a group                              4,393                 0         4,393
------------------------------------------------------------------------------- ------------- ----------------- -------------


(2) Mr. Broadbent is a citizen of the United Kingdom.


                                  (Page I - 2)