##### 



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; and



|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: August 8, 2003 |  | /s/ D. Keith Grossman  
|                     |  |                        
|                     |  | D. Keith Grossman,     
|                     |  | Chief Executive Officer

24



---



##### 



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:



| | b) |  | 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;         
| | -- |  | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|
| | c) |  | 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                                                                                          
|
| | d) |  | 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; and



|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):
|-- |  | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------



| | b) |  | 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
| | -- |  | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|
| | c) |  | 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: August 8, 2003 |  | /s/ M. Wayne Boylston                         
|                     |  |                                               
|                     |  | M. Wayne Boylston                             
|                     |  | Senior Vice President, Chief Financial Officer

25