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. 1)

                              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)

                                  June 29, 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               13,201,049
  OWNED BY EACH
 REPORTING PERSON
       WITH
                   ------------------------------------------------------------

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

                   9.    SOLE DISPOSITIVE POWER
                              15,932,828
                   ------------------------------------------------------------

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

11.    AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
       15,932,828
-------------------------------------------------------------------------------

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

13.    PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
       29.2%
-------------------------------------------------------------------------------

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 Items 4 and
5 of the initial Schedule 13D.

     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 4.    Purpose of Transactions.

      Item 4 is hereby amended and restated in its entirety as follows:

     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

                                 (Page 3 of 8)


("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.  Prior to the
Merger, the Reporting Person was the majority stockholder of Cardiosystems.

     The  following  is a summary of the  principal  terms of the  Merger.  This
summary is qualified in its entirety by reference to the  definitive  agreements
referred to herein and filed as exhibits to the initial Schedule 13D.

     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. 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"),  and (ii) a Registration  Rights  Agreement,  dated October 3, 2000
(the "Registration Rights Agreement").

     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

                                 (Page 4 of 8)


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. In accordance with the terms of the Registration
Rights  Agreement,  effective June 15, 2001, the Company caused to be registered
for resale by the Reporting Person 4,828,240 shares of Common Stock.

     Additionally,  before the Merger,  the  Reporting  Person  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 the  Reporting
Person. 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  remained  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.

                                 (Page 5 of 8)


     As   previously   announced,   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.

     Item 5 is hereby amended and restated in its entirety as follows:

     (a) As a result of the Merger,  the Reporting  Person became the beneficial
owner  of  19,352,828  shares  of  Common  Stock  of the  Company,  representing
approximately 35.4% of the outstanding Common Stock of the Company at that time.
This percentage  amount was based upon 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).  On June 29,
2001 and July 2, 2001,  the  Reporting  Person sold an  aggregate  of  3,400,000
shares of Common Stock in open market transactions.  In addition,  in July 2001,
the  Reporting  Person  transferred  20,000  shares of Common  Stock to a former
officer of Cardiosystems  pursuant to a transition  agreement executed with such
former officer. As a result of the foregoing transactions,  the Reporting Person
now  owns  15,932,828  shares  of  Common  Stock  which  represent  29.2% of the
outstanding  Common  Stock  of the  Company  based  on the  total  Common  Stock
outstanding as reported on the Company's  Quarterly  Report on Form 10-Q for the
period ended March 31, 2001. Of the 15,932,828  shares of Common Stock currently
owned by the Reporting Person,  (i) 34,902 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, and (ii) 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.  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.

                                 (Page 6 of 8)


     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  below 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.


     The  Reporting  Person has  affected the  following  open market sales with
respect to the Common Stock since the filing of the initial Schedule 13D:

-------------------------------------------------------------------------------
           Date                       Amount                Price per Share
-------------------------------------------------------------------------------
          6/29/01                    500,000                    $14.90
-------------------------------------------------------------------------------
          6/29/01                    500,000                    $15.45
-------------------------------------------------------------------------------
          7/02/01                    500,000                    $14.90
-------------------------------------------------------------------------------
          7/02/01                   1,900,000                   $14.65
-------------------------------------------------------------------------------

     In  addition  to the  foregoing,  Mr.  Frank  Jungers,  a  director  of the
Reporting  Perosn,  sold on June 20,  2001,  in open market  transactions  8,228
shares at $11.00 per share and 2,000 shares at $11.03249 per share.

(d) None.

(e)   Not applicable.



                                 (Page 7 of 8)



                                   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:  July 5, 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
                                                            -------------------------------------------------
                                                                         Shares Underlying
                                                                              Options                Total
 Name/Present Principal                                     Shares Held   Exercisable Prior       Beneficial
Occupation or Employment       Business Address              Outright      to July 5, 2001         Ownership
-------------------------------------------------------------------------------------------------------------
Samuel W. Bodman, III         Cabot Corporation                       0                  0                 0
Formerly Chairman and         75 State Street
Chief Executive Officer       Boston, Massachusetts
of Cabot Corporation.         02109
-------------------------------------------------------------------------------------------------------------
Peter O. Crisp
Vice Chairman of
Rockefeller Financial                                                 0                  0                 0
Services, Inc.
-------------------------------------------------------------------------------------------------------------
Frank Jungers                 822 NW Murrray
Private consultant on         Suite 242
business and energy           Portland, Oregon                        0                835               835
matters.                      97229
-------------------------------------------------------------------------------------------------------------
Jim P. Manzi
Currently involved in
number of technology
startup ventures,                                                     0                  0                 0
primarily relating to
the Internet.
-------------------------------------------------------------------------------------------------------------
Robert A. McCabe              Pilot Capital Corporation
Chairman of Pilot             444 Madison Avenue
Capital Corporation.          Suite 2103                          9,393                835            10,228
                              New York, New York 10022
-------------------------------------------------------------------------------------------------------------
Robert W. O'Leary         PacifiCare Health Systems, Inc.             0                  0                 0
President and Chief
Executive Officer of      3120 Lake Center Drive
PacifiCare Health         Santa Ana, California
Systems Inc.              92704
-------------------------------------------------------------------------------------------------------------
Hutham S. Olayan          Suite 1100
President and director    505 Park Avenue
of Olayan America         New York, New York 10022                9,393                835            10,228
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

                                  (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                Total
 Name/Present Principal                                     Shares Held   Exercisable Prior       Beneficial
Occupation or Employment       Business Address              Outright      to July 5, 2001         Ownership
-------------------------------------------------------------------------------------------------------------
Theo Melas-Kyriazi(2)                                             2,960             16,700            19,660
Vice President and Chief
Financial Officer of
Thermo Electron
-------------------------------------------------------------------------------------------------------------
Guy Broadbent(3)                                                      0                  0                 0
Vice President of Thermo
Electron, President,
Optical Technologies
-------------------------------------------------------------------------------------------------------------
Barry S. Howe                                                         0                  0                 0
Vice President of Thermo
Electron, President,
Measurement and Control
-------------------------------------------------------------------------------------------------------------
Colin Maddix                                                          0                  0                 0
Vice President of Thermo
Electron, President,
Life Sciences
-------------------------------------------------------------------------------------------------------------
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                21,746             19,205            40,951
group
-------------------------------------------------------------------------------------------------------------


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

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