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                                                                  EXHIBIT 10.9.1

                              AMENDMENT NO. 2 TO
                               SERVICE AGREEMENT
                                        
CardioDynamics International Corporation (the "Company") and Rivertek Medical
Systems, Inc. ("Rivertek") entered into a Service Agreement dated as of July 1,
1995 which was amended on July 25, 1997 (the "Agreement").  This Amendment No. 2
further amends the Agreement.  Dennis G. Hepp ("Hepp") is also a party to this
Amendment No. 2.  Capitalized terms not otherwise defined herein shall have the
meanings given in the Agreement.

  1.  As part of the Services, Rivertek shall make Hepp available to provide
engineering and management services including on-site hours through October 16,
2001 (extendable upon agreement of all parties) to accomplish certain
Engineering and Product Development objectives.

  2.  Hepp shall be a Company officer with the title of Chief Technology Officer
and with the powers and duties of such officer position.  The Company shall
provide coverage for Hepp under its directors and officers liability insurance
policy.  The Company shall indemnify Hepp against claims as it would any other
Company officer.

  3.  Hepp shall provide all services as a Rivertek Employee, and shall for all
purposes not be, and shall not be treated as being, a Company employee.  He
shall receive no Company fringe benefits.  Payments with respect to his hours
worked shall be to Rivertek (which shall be solely responsible for cash
compensation to Hepp as its employee, and for all tax withholding on Rivertek's
cash compensation to Hepp).

  4.  To avoid conflict of interest, Hepp shall not be responsible, within the
Company, for awarding work to or approving payment to Rivertek.  These functions
shall be handled by the Company's Chief Executive Officer.

  5.  The hourly rate payable by the Company to Rivertek for Hepp's time for the
duration of the special arrangement contemplated by this Amendment No. 2 shall
be Rivertek's rate for Hepp's time on Rivertek's standard hourly rate list.
Although the average rate list may be changed quarterly, in no event will Hepp's
full list rate exceed the average rate Rivertek then actually charges other
Rivertek clients for Hepp's time.  Hepp's travel time is billable to the Company
unless he works for other Rivertek clients while traveling.

  6.  To further incentivize Hepp, the Company shall on October 16, 1998 grant
Hepp a nonqualified stock option under the Company's 1995 Stock Option/Stock
Issuance Plan to purchase 90,000 shares of Company Common Stock at an exercise
price equal to that day's fair market value of the Company Common Stock.  The
Option shall expire on the earlier of October 16, 2008, or 90 days after
successful completion of contracted service to the Company. The Option shall
vest in a series of successive equal annual installments over each of the first
three (3) years of service completed by the Optionee commencing October 16,
1998.  Vesting shall continue unless, in the Company's opinion, Optionee
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declines to accept substantially all fair and reasonable services requested by
CDIC, does not perform satisfactorily, does not comply with Company's security
requirements or other applicable rules and regulations, or if the Company, for
other good cause relating to the performance of services by Hepp, terminates
this Service Agreement between the Company and Rivertek Medical Systems, Inc.

  7.  Hepp shall enter into a Company Consulting Services Agreement, which
contains proprietary-information and intellectual-property-assignment provisions
consistent with those applicable to Rivertek in the Agreement.

  8.  Rivertek's agreement in Section 8.10 of the Agreement shall expire no
sooner than nine months after the end of Hepp's tenure as Chief Technology
Officer.  Such agreement shall also apply to Hepp, as if he were Rivertek, from
now until nine months after the end of Hepp's tenure as Chief Technology
Officer.

  9.  The parties agree that Hepp shall benefit from and be bound by Article
VIII of the Agreement, with respect to this Agreement No. 1.  Hepp's address for
notice is c/o Rivertek.

  10.  Except as expressly set forth herein, the Agreement remains unchanged and
in full force and effect.

  Dated: October 16, 1998
                                       CARDIODYNAMICS INTERNATIONAL
                                       CORPORATION


                                           /s/ Michael K. Perry
                                       By: ________________________________
                                               Michael K. Perry
                                               Chief Executive Officer


                                       RIVERTEK MEDICAL SYSTEMS, INC.


                                           /s/ Dennis G. Hepp
                                       By: ________________________________
                                               Dennis G. Hepp
                                               Managing Director