UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

                                  SCHEDULE 13G

                   Under the Securities Exchange Act of 1934
                               (Amendment No. 5)*

                              Thoratec Corporation
                                (Name of Issuer)

                                  Common Stock
                         (Title of Class of Securities)

                                   885175307
                                 (CUSIP Number)

                               December 31, 2002
            (Date of Event Which Requires Filing of this Statement)

Check the appropriate box to designate the rule pursuant to which this Schedule
is filed:

      |_|   Rule 13d-1(b)
      |X|   Rule 13d-1(c)
      |_|   Rule 13d-1(d)

*The remainder of this cover page shall be filled out for a reporting person's
initial filing on this form with respect to the subject class of securities, and
for any subsequent amendment containing information which would alter the
disclosures provided in a prior cover page.

The information required in the remainder of this cover page shall not be deemed
to be "filed" for the purpose of Section 18 of the Securities Exchange Act of
1934 ("Act") or otherwise subject to the liabilities of that section of the Act
but shall be subject to all other provisions of the Act (however, see the
Notes).



CUSIP No. 885175307                    13G
--------------------------------------------------------------------------------
1.    NAME OF REPORTING PERSONS
      I.R.S. IDENTIFICATION NO. OF ABOVE PERSONS (ENTITIES ONLY)

      Peter R. Kellogg
--------------------------------------------------------------------------------
2.    CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*                  (a) [_]
                                                                         (b) [_]

--------------------------------------------------------------------------------
3.    SEC USE ONLY


--------------------------------------------------------------------------------
4.    CITIZENSHIP OR PLACE OF ORGANIZATION

      United States
--------------------------------------------------------------------------------
               5.    SOLE VOTING POWER

                     3,385,700
               -----------------------------------------------------------------
  NUMBER OF    6.    SHARED VOTING POWER
   SHARES
 BENEFICIALLY        300,000
  OWNED BY     -----------------------------------------------------------------
    EACH       7.    SOLE DISPOSITIVE POWER
  REPORTING
   PERSON            3,385,700
    WITH       -----------------------------------------------------------------
               8.    SHARED DISPOSITIVE POWER

                     300,000
--------------------------------------------------------------------------------
9.    AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

      3,685,700
--------------------------------------------------------------------------------
10.   CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES*

                                                                          [_]

--------------------------------------------------------------------------------
11.   PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)

      6.7%
--------------------------------------------------------------------------------
12.   TYPE OF REPORTING PERSON*

      IN, HC
--------------------------------------------------------------------------------
                     *SEE INSTRUCTIONS BEFORE FILLING OUT!



CUSIP No. 885175307                    13G
--------------------------------------------------------------------------------
1.    NAME OF REPORTING PERSONS
      I.R.S. IDENTIFICATION NO. OF ABOVE PERSONS (ENTITIES ONLY)

      IAT Reinsurance Company Ltd.
--------------------------------------------------------------------------------
2.    CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*                  (a) [_]
                                                                         (b) [_]

--------------------------------------------------------------------------------
3.    SEC USE ONLY


--------------------------------------------------------------------------------
4.    CITIZENSHIP OR PLACE OF ORGANIZATION

      Bermuda
--------------------------------------------------------------------------------
               5.    SOLE VOTING POWER

                     3,183,600
               -----------------------------------------------------------------
  NUMBER OF    6.    SHARED VOTING POWER
   SHARES
 BENEFICIALLY        NONE
  OWNED BY     -----------------------------------------------------------------
    EACH       7.    SOLE DISPOSITIVE POWER
  REPORTING
   PERSON            3,183,600
    WITH       -----------------------------------------------------------------
               8.    SHARED DISPOSITIVE POWER

                     NONE
--------------------------------------------------------------------------------
9.    AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

      3,183,600
--------------------------------------------------------------------------------
10.   CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES*

                                                                          [_]

--------------------------------------------------------------------------------
11.   PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)

      5.8%
--------------------------------------------------------------------------------
12.   TYPE OF REPORTING PERSON*

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



CUSIP No. 885175307

ITEM 1(a). NAME OF ISSUER:

            Thoratec Corporation ("Thoratec")

ITEM 1(b). ADDRESS OF ISSUER'S PRINCIPAL EXECUTIVE OFFICES:

            6035 Stoneridge Drive
            Pleasanton, CA 94588

ITEM 2(a). NAME OF PERSON FILING:

            This statement is filed on behalf of Peter R. Kellogg and IAT
Reinsurance Company Ltd. ("IAT"), a Bermuda corporation. Mr. Kellogg is the sole
owner of IAT's voting stock, is a member of IAT's board of directors, and is the
President and CEO of IAT. A joint filing agreement of Mr. Kellogg and IAT is
attached hereto as Exhibit A.

            This statement relates to 3,183,600 shares of Thoratec held by IAT
and its wholly-owned subsidiaries, 300,000 shares of Thoratec held by a
foundation controlled by Mr. Kellogg and his wife, plus an additional 202,100
shares held by Mr. Kellogg and by companies controlled by Mr. Kellogg. Mr.
Kellogg has sole dispositive and voting power with respect to the shares of
Thoratec owned by IAT and its subsidiaries. Mr. Kellogg disclaims beneficial
ownership of the shares held by his wife and by IAT and its subsidiaries, and
this statement should not be deemed to be an admission that Mr. Kellogg is a
member of any "group" within the meaning of Section 13(d)(3) of the Securities
Exchange Act of 1934, as amended, and the rules and regulations thereunder.

ITEM 2(b). ADDRESS OF PRINCIPAL BUSINESS OFFICE OR, IF NONE, RESIDENCE:

            120 Broadway, New York, NY 10271

ITEM 2(c). CITIZENSHIP:

            IAT is a Bermuda corporation, and Peter R. Kellogg is a citizen of
            the United States.

ITEM 2(d). TITLE OF CLASS OF SECURITIES:

            Common Stock

ITEM 2(e). CUSIP NUMBER:

            885175307



CUSIP No. 885175307

ITEM 3. IF THIS STATEMENT IS FILED PURSUANT TO RULE 13d-1(b), OR 13d-2(b) OR
        13d-2(c), CHECK WHETHER THE PERSON FILING IS A:

            N/A

ITEM 4. OWNERSHIP

      (a)   AMOUNT BENEFICIALLY OWNED: 3,685,700 shares

      (b)   PERCENT OF CLASS: 6.7%

      (c)   NUMBER OF SHARES AS TO WHICH SUCH PERSON HAS:

            (i)   Sole power to vote or to direct the vote: 3,385,700 shares

            (ii)  Shared power to vote or to direct the vote: 300,000

            (iii) Sole power to dispose or to direct the disposition of:
                  3,385,700 shares

            (iv)  Shared power to dispose or to direct the disposition of:
                  300,000

ITEM 5. OWNERSHIP OF FIVE PERCENT OR LESS OF A CLASS

            If this statement is being filed to report the fact that as of the
            date hereof the reporting person has ceased to be the beneficial
            owner of more than 5 percent of the class of securities, check the
            following: |_|

ITEM 6. OWNERSHIP OF MORE THAN FIVE PERCENT ON BEHALF OF ANOTHER PERSON

            The non-voting stockholders of IAT have the right to participate in
            the receipt of dividends from, or proceeds from the sale of, the
            shares held by them in accordance with their ownership interest in
            IAT.

ITEM 7. IDENTIFICATION AND CLASSIFICATION OF THE SUBSIDIARY WHICH ACQUIRED THE
        SECURITY BEING REPORTED ON BY THE PARENT HOLDING COMPANY

            See Exhibit B.

ITEM 8. IDENTIFICATION AND CLASSIFICATION OF MEMBERS OF THE GROUP

            Not Applicable

ITEM 9. NOTICE OF DISSOLUTION OF GROUP

            Not Applicable



CUSIP No. 885175307

ITEM 10. CERTIFICATION

            By signing below I certify that, to the best of my knowledge and
belief, the securities referred to above were not acquired and are not held for
the purpose of or with the effect of changing or influencing the control of the
issuer of the securities and were not acquired and are not held in connection
with or as a participant in any transaction having that purpose or effect.



CUSIP No. 885175307

                                    SIGNATURE

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

                                                    IAT REINSURANCE COMPANY LTD.

Dated: February 20, 2004
       New York, New York                           By: /s/ Peter R. Kellogg
                                                        ------------------------
                                                        Name: Peter R. Kellogg
                                                        Title: President and CEO

Dated: February 20, 2004
       New York, New York                               /s/ Peter R. Kellogg
                                                    ----------------------------
                                                      Peter R. Kellogg



CUSIP No. 885175307

                                                                       Exhibit A

                             JOINT FILING AGREEMENT

            In accordance with the provisions of Rule 13d-1(k) under the
Securities Exchange Act of 1934, as amended, the undersigned hereby agree to
jointly prepare and file a Schedule 13G (including any future amendments
thereto) reporting each of the undersigned's ownership of securities of Thoratec
Corporation and further agree to the filing of this Agreement as an Exhibit
thereto. In addition, each party to this Agreement expressly authorizes each
other party to file on its behalf any and all amendment to such Schedule 13G.
The undersigned acknowledge that each shall be responsible for the timely filing
of such amendments, and for the completeness and accuracy of the information
concerning him or it contained therein, but shall not be responsible for the
completeness and accuracy of the information concerning the other, except to the
extent that he or it knows or has reason to believe that such information is
inaccurate.

                                                    IAT REINSURANCE COMPANY LTD.

Dated: February 20, 2004
       New York, New York                           By: /s/ Peter R. Kellogg
                                                        ------------------------
                                                        Name: Peter R. Kellogg
                                                        Title: President and CEO

Dated: February 20,2004
       New York, New York                               /s/ Peter R. Kellogg
                                                    ----------------------------
                                                      Peter R. Kellogg



CUSIP No. 885175307

                                                                       Exhibit B

                                     ITEM 7

            IAT is the relevant subsidiary for which Peter R. Kellogg may be
considered a control person.