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)

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

                                February 14, 2001
                  --------------------------------------------
              (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 8 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               16,686,555
  OWNED BY EACH
 REPORTING PERSON
       WITH
                   ------------------------------------------------------------

                   8.    SHARED VOTING POWER
                              2,731,779
                   ------------------------------------------------------------

                   9.    SOLE DISPOSITIVE POWER
                              19,418,334
                   ------------------------------------------------------------

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

11.    AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
       19,418,334
-------------------------------------------------------------------------------

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

13.    PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
       35.5%
-------------------------------------------------------------------------------

14.    TYPE OF REPORTING PERSON*

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





ITEM 1.    Security of the Issuer.

     The securities to which this statement relates are 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").
The principal  executive  offices of the Company are located at 6035  Stoneridge
Drive, Pleasanton, California 94588.

ITEM 2.    Identity and Background.

     This statement is being filed by Thermo  Electron  Corporation,  a Delaware
corporation ("Thermo Electron"). Thermo Electron is sometimes referred to herein
as the "Reporting Person."

     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 of 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 3.    Source and Amount of Funds or Other Consideration.

      The Common Stock acquired by the Reporting Person was acquired on February
14, 2001, in connection with the merger (the "Merger") of Lightning  Acquisition
Corp., a Massachusetts  corporation  and wholly owned  subsidiary of the Company
("Merger  Sub"),  with and  into  Thermo  Cardiosystems  Inc.,  a  Massachusetts
corporation  ("Cardiosystems"),  pursuant to that certain  Agreement and Plan of
Merger (the "Merger  Agreement"),  dated as of October 3, 2000, by and among the
Company,  Merger  Sub,  Cardiosystems  and  the  Reporting  Person.  The  Merger
Agreement is filed as Exhibit 99.1 hereto.  Prior to the Merger,  the  Reporting
Person was the majority stockholder of Cardiosystems.

      Pursuant to the terms of the Merger  Agreement,  each outstanding share of
Cardiosystems  common stock was converted into the right to receive 0.835 shares
of  Common  Stock  of  the  Company.  Accordingly,  the  outstanding  shares  of
Cardiosystems common stock owned by the Reporting Person were converted into the
number of shares of Common Stock of the Company acquired by the Reporting Person
on February 14, 2001.

ITEM 4.    Purpose of Transactions.

      The following is a summary of the principal terms of the transaction. This
summary is qualified in its entirety by reference to the  definitive  agreements
referred to herein and filed as exhibits hereto.

      The  Merger  Agreement  was  entered  into  by the  Company,  Merger  Sub,
Cardiosystems and the Reporting Person as of October 3, 2000. The closing of the
Merger occurred on February 14, 2001. In connection with the Merger,  the former
stockholders of Cardiosystems  received, in the aggregate,  32,213,812 shares of
Common Stock of the Company.

      In  connection  with  the  Merger  Agreement,  and as a  condition  to the
consummation  of the Merger,  the Company and the Reporting  Person entered into
(i)  a  Shareholder   Agreement,   dated  October  3,  2000  (the   "Shareholder
Agreement"),  which is attached  hereto as Exhibit 99.2 and (ii) a  Registration
Rights Agreement,  dated October 3, 2000 (the "Registration  Rights Agreement"),
which is attached hereto as Exhibit 99.3.


      Pursuant to the Shareholder Agreement,  the Company agreed that, following
the Merger, as long as the Reporting Person  beneficially owns voting securities
of the  Company  representing  at least  10% of the  voting  power of all of the
Company's  voting  securities  outstanding,  the Company will take all necessary
action to cause a nominee of the Reporting Person to be elected to the Company's
board of directors.  The Reporting  Person has  designated  its Chief  Financial
Officer,  Theo  Melas-Kyriazi,  to serve as its  initial  representative  on the
Company's board of directors. Additionally, the Reporting Person agreed that, so
long as it beneficially  owns voting  securities of the Company  representing at
least  5% of  the  voting  power  of  all of  the  Company's  voting  securities
outstanding,  the Reporting Person will not (i) acquire any voting securities of
the Company without prior consent of the board of directors of the Company, (ii)
sell or otherwise transfer any shares of Common Stock of the Company received in
the Merger  prior to the date four  months  following  the  consummation  of the
Merger,  (iii) sell or otherwise  transfer more than 25% of the shares of Common
Stock of the Company  received in the Merger prior to the first  anniversary  of
the consummation of the Merger, (iv) sell or otherwise transfer more than 50% of
the shares of Common  Stock of the Company  received in the Merger  prior to the
date eighteen months  following the  consummation of the Merger,  or (v) sell or
transfer  any  shares of Common  Stock of the  Company in  privately  negotiated
transactions if, after giving effect to such transactions,  the transferee would
own securities of the Company  representing more than 10% of the voting power of
all of the Company's voting  securities  outstanding.  The Reporting Person also
agreed that,  with respect to the Common Stock of the Company it received in the
Merger,  it will (i) cause such shares of Common Stock to appear or otherwise be
counted as present for  purposes  of  establishing  a quorum at any  shareholder
meeting of the Company and (ii) provide the Company's management with a proxy or
consent to vote such shares of Common Stock owned by the Reporting  Person,  but
not  more  than a  number  of  shares  representing  5% of the  voting  power of
securities of the Company outstanding at the closing of the Merger.

      Pursuant to the terms of the Registration  Rights  Agreement,  the Company
agreed to (i) file with the Securities and Exchange  Commission  (the "SEC") and
use its reasonable  best efforts to cause to become  effective an `evergreen' or
`shelf'  registration  statement  registering for resale by the Reporting Person
the Common Stock of the Company  received by the Reporting Person in the Merger,
(ii) file a registration statement,  or a post-effective  amendment to the shelf
registration  statement,  for an  underwritten  offering of the shares of Common
Stock of the Company  received by the Reporting  Person in the Merger at various
times, and (iii) provide the Reporting Person the right to include the shares of
Common Stock of the Company  received by the  Reporting  Person in the Merger in
any  registration  statement  filed by the  Company  with the  SEC,  other  than
registration statements relating to employee plans and acquisitions.  The timing
of the effectiveness of the `shelf'  registrations  corresponds to the timing of
the  lapse  of  the  transfer   restrictions  under  the  Shareholder  Agreement
applicable  to the  shares  of  Common  Stock  of the  Company  received  by the
Reporting Person in the Merger.


      Additionally, the Reporting Person has granted certain officers, directors
and  employees  of the  Reporting  Person  options to purchase a total of 68,000
shares of Cardiosystems common stock owned by Thermo Electron before the Merger.
Those  officers,  directors  and  employees  are  entitled  to have the  Company
register   the  shares  of  Common   Stock  of  the  Company  into  which  those
Cardiosystems shares were converted in the Merger.

      Immediately  prior to the  consummation of the Merger,  Cardiosystems  had
$54.9 million of 4 3/4%  Subordinated  Convertible  Debentures  due 2004 (the "4
3/4%  Debentures")  outstanding.  The 4 3/4%  Debentures were  convertible  into
shares  of  Cardiosystems  common  stock  at a price  of  $31.415  per  share of
Cardiosystems common stock. Following the consummation of the Merger, the 4 3/4%
Debentures remain obligations of Cardiosystems,  but are convertible into shares
of Common  Stock of the  Company,  at a  conversion  price of $37.623 per share,
which is $31.415 divided by the 0.835 merger exchange ratio.

      Additionally,  the 4 3/4%  Debentures  are  guaranteed  by  the  Reporting
Person,  which guarantee  remains in effect after the Merger.  Cardiosystems has
agreed to reimburse the Reporting  Person for any payments made by the Reporting
Person under such guarantee.  Pursuant to the terms of the Merger Agreement, the
Company has obtained a standby  letter of credit in the amount of $45 million to
support the repayment of the 4 3/4%  Debentures  and to reduce the prospect that
the  Reporting  Person will be required to pay any amount under its guarantee of
the 4 3/4% Debentures.

     As previously announced in January 2000, the Reporting Person has initiated
a  restructuring,  of which  the  Merger  is a  component,  to focus on its core
instruments business.  Accordingly, the Reporting Person may consummate the sale
of shares of Common Stock from time to time in accordance  with the  Shareholder
and Registration  Rights Agreements.  Any such sales will be dependent upon then
current market conditions and other relevant considerations,  and may be made on
the  open  market,  in  privately  negotiated  transactions  or in one  or  more
underwritten offerings. Except as described in this Item 4, the Reporting Person
does not have any current  plans or proposals  that relate to or would result in
any of the events  described in paragraphs (a) through (j) of Item 4 of Schedule
13D.

ITEM 5.    Interest in Securities of the Issuer.

      (a) As a result of the  Merger,  the  Reporting  Person is the  beneficial
owner  of  19,418,334  shares  of  Common  Stock  of the  Company,  representing
approximately  35.5%  of the  outstanding  Common  Stock  of the  Company.  This
percentage amount reflects the 32,213,812 shares of Common Stock of the Company
issued in  connection  with the  Merger,  as  disclosed  by the  Company  in its
registration  statement  on Form S-4  (Commission  File No.  333-49120).  Of the
19,418,334  shares of Common  Stock owned by the  Reporting  Person,  (i) to the
knowledge  of  the  Reporting   Person,   65,506  shares  of  Common  Stock  are
beneficially  owned by the other  persons named in Item 2, (ii) 56,780 shares of
Common  Stock are  subject  to options to  acquire  such  shares  granted by the
Reporting Person pursuant to its director and employee stock option plans, (iii)
39,869 shares of Common Stock are issuable upon the  conversion by the Reporting
Person of $1,500,000  principal  amount of the 4 3/4% Debentures held by it, and
(iv)  Reporting  Person has agreed to grant  16,700  shares of Common Stock to a
former officer of Cardiosystems pursuant to a transition agreement executed with
such former officer. Information with respect to the beneficial ownership of the
shares of  Common  Stock of the  other  persons  named in Item 2 is set forth in
Appendix  A.  Except as set forth in this Item 5, to the best  knowledge  of the
Reporting Person,  none of the parties named in Item 2 owns any of the Company's
Common Stock.


      (b) With  respect  to  2,731,779  shares  of Common  Stock of the  Company
beneficially  owned by the Reporting  Person,  the  Reporting  Person shares the
power to vote all of such shares with the  Company  pursuant to the  Shareholder
Agreement,  as  more  fully  described  in Item 4  above.  With  respect  to the
remainder of the shares of Common Stock of the Company beneficially owned by the
Reporting  Person,  the  Reporting  Person  has the sole  power to vote all such
shares.  Subject  to the  terms  of the  Shareholder  Agreement,  as more  fully
described in Item 4 above, the Reporting Person has the sole power to dispose of
the shares of Common Stock  beneficially owned by it. With respect to the shares
of Common Stock of the Company  beneficially owned by the other persons named in
Item 2,  except as set forth in  Appendix A, each such person has the sole power
to vote all of such shares and the sole power to dispose of all of such shares.

      Item 1 sets forth the Company's name and state of incorporation along with
the address of its  principal  business  and  principal  office.  The  Company's
principal business is the research, development,  manufacturing and marketing of
medical devices for circulatory support and vascular graft applications.  To the
best knowledge of the Reporting Person,  during the last five years, the Company
(i) has  not  been  convicted  in any  criminal  proceeding  (excluding  traffic
violations  or  similar  misdemeanors)  and  (ii)  was  not a  party  to a civil
proceeding of a judicial or  administrative  body of competent  jurisdiction  as
result  of which it was or is  subject  to 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.

      (c) Except as described  above in this Item 5 and in Item 4, which item is
incorporated  herein by  reference,  neither  the  Reporting  Person nor, to the
knowledge of the Reporting  Person,  any person named in Appendix A beneficially
has effected any transactions in Common Stock during the past 60 days.

      (d) None.

      (e) Not applicable.


ITEM 6. Contracts, Arrangements, Understandings or Relationships with Respect to
Securities of the Issuer.

     The  responses  to  Item 3,  Item 4,  Item 5,  the  Merger  Agreement,  the
Shareholder  Agreement and the  Registration  Rights  Agreement are incorporated
herein by reference.

ITEM 7.    Material to be Filed as Exhibits.

     The following documents are filed as a Exhibits to this Schedule 13D.

Exhibit No.    Description

99.1 Agreement  and Plan of Merger,  dated as of  October 3, 2000,  by and among
     Thoratec  Laboratories  Corporation,  Lightning  Acquisition Corp.,  Thermo
     Cardiosystems Inc. and Thermo Electron Corporation (1)

99.2 ShareholderAgreement,  dated as of October 3, 2000, by and between Thoratec
     Laboratories Corporation and Thermo Electron Corporation.

99.3 Registration Rights Agreement,  dated as of October 3, 2000, by and between
     Thoratec Laboratories Corporation and Thermo Electron Corporation.

----------------------
(1)  Incorporated  by  reference  from the  Registration  Statement  on form S-4
     (File No. 333-49120) of Thoratec Corporation.





                                  SIGNATURES

     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:  February 23, 2001          THERMO ELECTRON CORPORATION


                                   By:  /s/ Theo Melas-Kyriazi
                                        ------------------------------------
                                   Name:     Theo Melas-Kyriazi
                                   Title:    Vice President and Chief Financial
                                             Officer





                                  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
                                                     --------------------------------------------------------------------
 Name/Present Principal       Business Address          Shares           Shares Underlying          Total
Occupation or Employment                             Held Outright            Options             Beneficial
                                                                           Exercisable Prior      Ownership
                                                                           to April 15, 2001
--------------------------------------------------------------------------------------------------------------------------
Samuel W. Bodman              Cabot Corporation                     0              0                   0
Chairman and Chief            75 State Street
Executive Officer of          Boston, Massachusetts
Cabot Corporation.            02109
-------------------------------------------------------------------------------------------------------------------------

Peter O. Crisp                                                      0              0                   0
Vice Chairman of
Rockefeller Financial
Services, Inc.
-------------------------------------------------------------------------------------------------------------------------
Elias P. Gyftopoulos          Massachusetts Institute          11,192          3,131              14,324
Professor Emeritus of         of Technology
the Massachusetts             Room 24-109
Institute of                  77 Massachusetts Avenue
Technology.                   Cambridge, Massachusetts
                              02139
-------------------------------------------------------------------------------------------------------------------------
Frank Jungers                 822 NW Murrray                   10,229            835              11,064
Private consultant on         Suite 242
business and energy           Portland, Oregon 97229
matters.
-------------------------------------------------------------------------------------------------------------------------
Jim P. Manzi                                                        0              0                   0
Currently involved in
number of technology
startup ventures,
primarily relating to
the Internet.
-------------------------------------------------------------------------------------------------------------------------
Robert A. McCabe              Pilot Capital Corporation         9,394            835              10,229
Chairman of Pilot             444 Madison Avenue
Capital Corporation.          Suite 2103
                              New York, New York 10022
-------------------------------------------------------------------------------------------------------------------------
Robert W. O'Leary             PacifiCare Health Systems, Inc.       0              0                   0
President and Chief           3120 Lake Center Drive
Executive Officer of          Santa Ana, California 92704
PacifiCare Health
Systems Inc.
-------------------------------------------------------------------------------------------------------------------------
Hutham S. Olayan              Suite 1100                        9,394            835              10,229
President and director        505 Park Avenue
of Olayan America             New York, New York 10022
Corporation.
-------------------------------------------------------------------------------------------------------------------------
Richard F. Syron                                                    0              0                   0
Chief Executive Officer
and Chairman of the
Board of Thermo Electron
-------------------------------------------------------------------------------------------------------------------------
Marijn E. Dekkers(1)                                                0              0                   0
President, Chief
Operating Officer and
Director of Thermo
Electron
-------------------------------------------------------------------------------------------------------------------------


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






Executive Officers Who are Not Directors

      No person is a controlling stockholder of Thermo Electron.



                                                                                             
                                                                Beneficial Ownership of Shares
                                                                 of the Company Common Stock
                                                     --------------------------------------------------------------------
 Name/Present Principal       Business Address          Shares           Shares Underlying          Total
Occupation or Employment                             Held Outright            Options             Beneficial
                                                                           Exercisable Prior      Ownership
                                                                           to April 15, 2001
-------------------------------------------------------------------------------------------------------------------------
Theo Melas-Kyriazi(2)                                      2,961              16,700                  19,661
Vice President and
Chief Financial Officer
of Thermo Electron
-------------------------------------------------------------------------------------------------------------------------
Guy Broadbent                                                  0                   0                       0
Vice President, Optical
Technologies of Thermo
Electron
-------------------------------------------------------------------------------------------------------------------------
Barry S. Howe                                                  0                   0                       0
Vice President,
Measurement and Control
of Thermo Electron
-------------------------------------------------------------------------------------------------------------------------
Colin Maddix                                                   0                   0                       0
Vice President, Life
Sciences of Thermo
Electron
-------------------------------------------------------------------------------------------------------------------------
Seth H. Hoogasian                                              0                   0                       0
Vice President and
General Counsel of
Thermo Electron
-------------------------------------------------------------------------------------------------------------------------
Peter E. Hornstra                                              0                   0                       0
Corporate Controller
and Chief Accounting
Officer of Thermo
Electron
-------------------------------------------------------------------------------------------------------------------------
All directors and current executive officers as a         43,170              22,336                  65,506
group
-------------------------------------------------------------------------------------------------------------------------


(2) Mr. Melas-Kyriazi is a citizen of Greece.