##### 



Exhibit 31.1

CERTIFICATION PURSUANT TO RULE 15d-14
OF THE SECURITIES EXCHANGE ACT OF 1934, AS AMENDED
AS ADOPTED PURSUANT TO
SECTION 302 OF THE SARBANES-OXLEY ACT OF 2002

I, D. Keith Grossman, Chief Executive Officer of Thoratec Corporation, certify
that:



|1. |  | I have reviewed this quarterly report on Form 10-Q of Thoratec
Corporation;                                                                                                                                                                                                                                                   
|-- |  | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|  
|2. |  | Based on my knowledge, this quarterly report does not contain any untrue
statement of a material fact or omit to state a material fact necessary to
make the statements made, in light of the circumstances under which such
statements were made, not misleading with respect to the period covered by
this quarterly report;
|  
|3. |  | Based on my knowledge, the financial statements, and other financial
information included in this quarterly report, fairly present in all
material respects the financial condition, results of operations and cash
flows of the registrant as of, and for, the periods presented in this
quarterly report;                   
|  
|4. |  | The registrants other certifying officers and I are responsible for
establishing and maintaining disclosure controls and procedures (as
defined in Exchange Act Rules 13a-15(e) and 15d-15(e)) for the registrant
and we have:                                                                                               



| | a) |  | designed such disclosure controls and procedures, or caused such
disclosure controls and procedures to be designed under our supervision,
to ensure that material information relating to the registrant,
including its consolidated subsidiaries, is made known to us by others
within those entities, particularly during the period in which this
quarterly report is being prepared;     
| | -- |  | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|
| | b) |  | evaluated the effectiveness of the registrants disclosure controls
and procedures and presented in this quarterly report our conclusions
about the effectiveness of the disclosure controls and procedures, as of
the end of the period covered by this quarterly report based on such
evaluation; and                                                                                      
|
| | c) |  | disclosed in this quarterly report any change in the registrants
internal control over financial reporting that occurred during the
registrants most recent fiscal quarter (the registrants fourth fiscal
quarter in the case of an annual report) that has materially affected,
or is reasonably likely to materially affect, the registrants internal
control over financial reporting.



|5. |  | The registrants other certifying officers and I have disclosed, based on
our most recent evaluation of internal control over financial reporting,
to the registrants auditors and the audit committee of the registrants
board of directors (or persons performing the equivalent functions):
|-- |  | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------



| | a) |  | all significant deficiencies and material weaknesses in the design or
operation of internal control over financial reporting which are
reasonably likely to adversely affect the registrants ability to
record, process, summarize and report financial information; and
| | -- |  | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|
| | b) |  | any fraud, whether or not material, that involves management or other
employees who have a significant role in the registrants internal
control over financial reporting.                                                                                               

|                        |  |                        
|----------------------- |  | -----------------------
|Date: November 10, 2003 |  | /s/ D. Keith Grossman  
|                        |  |                        
|                        |  | D. Keith Grossman,     
|                        |  | Chief Executive Officer

22



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##### 



CERTIFICATION PURSUANT TO RULE 15d-14
OF THE SECURITIES EXCHANGE ACT OF 1934, AS AMENDED
AS ADOPTED PURSUANT TO
SECTION 302 OF THE SARBANES-OXLEY ACT OF 2002

I, M. Wayne Boylston, Chief Financial Officer of Thoratec Corporation, certify
that:



|1. |  | I have reviewed this quarterly report on Form 10-Q of Thoratec
Corporation;                                                                                                                                                                                                                                                         
|-- |  | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|  
|2. |  | Based on my knowledge, this quarterly report does not contain any untrue
statement of a material fact or omit to state a material fact necessary to
make the statements made, in light of the circumstances under which such
statements were made, not misleading with respect to the period covered by
this quarterly report;      
|  
|3. |  | Based on my knowledge, the financial statements, and other financial
information included in this quarterly report, fairly present in all
material respects the financial condition, results of operations and cash
flows of the registrant as of, and for, the periods presented in this
quarterly report;                         
|  
|4. |  | The registrants other certifying officers and I are responsible for
establishing and maintaining disclosure controls and procedures (as
defined in Exchange Act Rules 13a-15(e) and 15d-15(e)) and internal
control over financial reporting (as defined in Exchange Act Rules 15(f)
and 15d-15(f)) for the registrant and we have:



| | a) |  | designed such disclosure controls and procedures, or caused such
disclosure controls and procedures to be designed under our supervision,
to ensure that material information relating to the registrant,
including its consolidated subsidiaries, is made known to us by others
within those entities, particularly during the period in which this
quarterly report is being prepared;     
| | -- |  | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|
| | b) |  | evaluated the effectiveness of the registrants disclosure controls
and procedures and presented in this quarterly report our conclusions
about the effectiveness of the disclosure controls and procedures, as of
the end of the period covered by this quarterly report based on such
evaluation; and                                                                                      
|
| | c) |  | disclosed in this quarterly report any change in the registrants
internal control over financial reporting that occurred during the
registrants most recent fiscal quarter (the registrants fourth fiscal
quarter in the case of an annual report) that has materially affected,
or is reasonably likely to materially affect, the registrants internal
control over financial reporting.



|5. |  | The registrants other certifying officers and I have disclosed, based on
our most recent evaluation of internal control over financial reporting,
to the registrants auditors and the audit committee of the registrants
board of directors (or persons performing the equivalent functions):
|-- |  | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------



| | a) |  | all significant deficiencies and material weaknesses in the design or
operation of internal control over financial reporting which are
reasonably likely to adversely affect the registrants ability to
record, process, summarize and report financial information; and
| | -- |  | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|
| | b) |  | any fraud, whether or not material, that involves management or other
employees who have a significant role in the registrants internal
control over financial reporting.                                                                                               

|                        |  |                                               
|----------------------- |  | ----------------------------------------------
|Date: November 10, 2003 |  | /s/ M. Wayne Boylston                         
|                        |  |                                               
|                        |  | M. Wayne Boylston                             
|                        |  | Senior Vice President, Chief Financial Officer

23