Document:

<PAGE>

                                                                     EXHIBIT 4.2
                                                                     -----------

================================================================================

                         REGISTRATION RIGHTS AGREEMENT

                                by and between

                   CardioDynamics International Corporation,

                           a California corporation

                                      and

              The Holders Identified on the Signature Page hereof
                        _______________________________

                          Dated as of August 13, 2001

================================================================================

<PAGE>

                               TABLE OF CONTENTS

<TABLE>
<CAPTION>
                                                                         Page
<S>                                                                      <C>
1. Registration Rights.................................................     2

   1.1  Definitions....................................................     2

   1.2  Shelf Registration.............................................     3

   1.3  Obligations of the Company.....................................     3

   1.4  Furnish Information............................................     5

   1.5  Representations and Warranties of the Company..................     5

   1.6  Indemnification................................................     6

   1.7  Rule 144 Reporting.............................................     8

   1.8  Blocking Notice................................................     9

   1.9  Holder Information.............................................     9

2. Miscellaneous.......................................................     9

   2.1  Termination of the Company's Obligations.......................     9

   2.2  Successors and Assigns.........................................    10

   2.3  Amendment and Waivers..........................................    10

   2.4  Notices........................................................    10

   2.5  Headings.......................................................    10

   2.6  Construction...................................................    10

   2.7  Entire Agreement...............................................    11

   2.8  Governing Law..................................................    11

   2.9  Counterparts...................................................    11

   2.10 Compliance.....................................................    11
</TABLE>

                                      (i)
<PAGE>

                      CARDIODYNAMICS INTERNATIONAL CORP.

                         REGISTRATION RIGHTS AGREEMENT

     THIS REGISTRATION RIGHTS AGREEMENT (the "Agreement"), dated as of August
13, 2001, is entered into by and between CardioDynamics International Corp., a
California corporation (the "Company"), and the shareholders of the Company
listed on the signature page hereof, (each a "Shareholder" and collectively the
"Shareholders").

                                   Recitals
                                   --------

     WHEREAS, Shareholders and the Allen E. Paulson Living Trust (the "Trust")
have entered into a certain stock purchase agreement, dated as of August 13,
2001 (the "Purchase_Agreement"), pursuant to which the Trust shall sell to
Shareholders, and Shareholders shall purchase from the Trust, up to 510,000
shares of common stock of the Company (the "Shares"); and

     WHEREAS, Shareholders desire to obtain certain registration rights
associated with such Shares, and the Company, as an inducement to Shareholders
to enter into the Purchase Agreement, desires to grant Shareholders such
registration rights, as more fully set forth in this Agreement.

     NOW, THEREFORE, in consideration of the mutual promises made in this
Agreement, the parties, intending to become legally bound, hereby agree as
follows:

                                   Agreement
                                   ---------

1.   Registration Rights.
     --------------------

     1.1  Definitions.
          -----------

          (a)  "Best Efforts" shall mean the efforts that a prudent Person
desirous of achieving a result would use under similar circumstances as the
Company to attempt to cause such result to be achieved as expeditiously as
possible.

          (b)  "Business Day" means any day except Saturday, Sunday and any day
which shall be a legal holiday or a day on which banking institutions in the
State of New York or California are authorized or required by law or other
government actions to close.

          (c)  "Holder" means any person owning of record Registrable Securities
that have not been sold to the public, or any assignee of record of such
Registrable Securities to whom rights under this Section 1 have been assigned in
                                                 ---------
accordance with this Agreement.

          (d)  "Person" means an individual or corporation, partnership, trust,
incorporated or unincorporated association, joint venture, limited liability
company, joint stock company, government (or an agency or subdivision thereof)
or other entity of any kind.

          (e)  "Proceeding" means an action, claim, suit, investigation or
proceeding (including, without limitation, an investigation or partial
proceeding, such as a deposition), whether commenced or threatened.
<PAGE>

          (f)  "Register," "registered," and "registration" refer to a
registration effected by preparing and filing a registration statement in
compliance with the Securities Act, and the declaration or ordering of
effectiveness of such registration statement.

          (g)  "Registrable Securities" means the Shares and any securities
issued or issuable in respect of such Shares by way of conversion, exchange,
stock dividend, split or combination, recapitalization, merger, consolidation,
other reorganization or otherwise until (1) such Shares have been disposed of
pursuant to an effective registration statement, (2) such Shares are sold
pursuant to Rule 144 or (3) such Shares are otherwise transferred and may be
resold without subsequent registration under the Securities Act.

     1.2  Shelf Registration.
          ------------------

          (a)  The Company will file as soon as practicable, and in no event
later than thirty (30) days after the Closing Date (as such term as defined in
the Purchase Agreement), a registration statement with the Securities and
Exchange Commission ("SEC") under the Securities Act of 1933, as amended
("Securities Act") for the sale and distribution of all of the Holders'
Registrable Securities and thereafter shall use its Best Efforts to secure the
effectiveness of such registration statement as soon as practicable thereafter,
but in any event prior to the ninetieth (90th) day after the Closing Date,
including but not limited to, responding to comments, if any, from the SEC
within ten (10) days of receipt of such comments.

          (b)  The Company will pay all of its expenses incurred in connection
with any registration, qualification and compliance requested hereunder
(excluding Holders' or brokers' discounts and commissions), including without
limitation all filing, registration and qualification, and accounting fees and
the fees and disbursements of counsel for the Company.

          (c)  The Company will use its Best Efforts to cause the registration
statement to remain effective until the earliest of (a) the date ending two (2)
years after the Closing Date, (b) the date on which all the Registrable
Securities have been resold in accordance with the Securities Act or (c) the
date on which each Holder of Registrable Securities is able to sell all of such
Holder's Registrable Securities in a single three (3) month period without
registration under the Securities Act pursuant to Rule 144.

     1.3  Obligations of the Company.  In order to effect the registration of
          --------------------------
any Registrable Securities under Section 1.2 of this Agreement, the Company
                                 -----------
will, as expeditiously as reasonably possible (and, in no event later than 30
days after the Closing Date with respect to the registration statement described
in subclause (a) of this Section 1.3:
                         -----------

          (a)  Prepare and file with the SEC a registration statement with
respect to such Registrable Securities, and use its Best Efforts to cause such
registration statement to become effective in accordance with Section 1.2(a)
above, and deliver to one counsel for all Holders a copy of such registration
statement promptly after the filing thereof.

          (b)  Prepare and file with the SEC such amendments and supplements to
such registration statement and the prospectus used in connection with such
registration statement, within ten (10) days of receipt of such comments, as may
be necessary to comply with the provisions of the Securities Act with respect to
the disposition of all securities covered by such registration statement and
provide a copy of each such amendment and supplement to one counsel for all
Holders promptly after the filing thereof.
<PAGE>

          (c)  Furnish to the Holders such number of copies of a prospectus in
conformity with the requirements of the Securities Act, and such other documents
as they may reasonably request in order to facilitate the disposition of the
Registrable Securities owned by them that are included in such registration
statement.

          (d)  Use its Best Efforts to register and qualify the securities
covered by such registration statement under such other securities or "blue sky"
laws of such jurisdictions as will be reasonably requested by the Holders,
provided that the Company will not be required in connection therewith or as a
condition thereto to qualify to do business or to file a general consent to
service of process in any such states or jurisdictions.

          (e)  Notify each Holder of Registrable Securities covered by such
registration statement at any time when a prospectus relating thereto is
required to be delivered under the Securities Act of the happening of any event
as a result of which the prospectus included in such registration statement, as
then in effect, includes an untrue statement of a material fact or omits to
state a material fact required to be stated therein or necessary to make the
statements therein not misleading in the light of the circumstances then
existing, and upon such notice the Company shall use its Best Efforts to
promptly correct such misstatement or omission and deliver to each Holder copies
of such corrected prospectus. The Company shall have the right, upon such
notice, to suspend the delivery of prospectuses included in such registration
statement from the date of notice until the date of such correction, subject to
the limitations set forth in Section 1.8. The period during which the Company is
                             -----------
required to keep any registration statement filed pursuant to Section 1.2
                                                              -----------
effective shall be extended for the amount of time required to amend such
registration statement and deliver such prospectus relating thereto.

          (f)  The Company shall use its Best Efforts to maintain designation
and quotation of all the Registrable Securities covered by the registration
statement on the Nasdaq National Market System or the Nasdaq SmallCap Market for
such Registrable Securities and, without limiting the generality of the
foregoing, to arrange for at least two market makers to register with the
National Association of Securities Dealers, Inc. as such with respect to such
Registrable Securities. The Company shall pay all fees and expenses in
connection with satisfying its obligation under this Section 1.3(f).
                                                     --------------

          (g)  The certificates representing the Shares shall bear the legend
set forth in the Transfer Agent Instruction of even date herewith (the "Transfer
Agent Instruction"). The Company shall use its Best Efforts to cause its counsel
to issue the letter attached as Exhibit I to the Transfer Agent Instruction to
transfer agent within three (3) Business Days of the date that the registration
statement is declared effective by the SEC (such date, the "Effective Date").
The Company agrees that following the Effective Date, it will, no later than
three (3) Business Days following the delivery by a Holder to the Company's
transfer agent of a certificate or certificates representing the Shares sold
with restrictive legends and such undertakings as are called for by the Transfer
Agent Instruction, cause its transfer agent to deliver to such Holder,
certificates representing such Shares which shall be free from all restrictive
and other legends.

          (h)  The Company shall notify the Holders of Registrable Securities to
be sold as promptly as reasonably possible (A) when the SEC notifies the Company
whether there will be a "review" of the registration statement and whenever the
SEC comments in writing on such registration statement (the Company shall
provide true and complete copies thereof and all written responses thereto to
each of the Holders); and (B) with respect to the registration statement or any
post-effective amendment, when the same has become effective; (i) of any request
by the SEC or any other federal or state governmental authority for amendments
or supplements to the registration statement or any prospectus constituting a
portion thereof or for additional information; (ii) of the issuance by the SEC
of any stop order suspending the effectiveness of the registration statement
covering any or all of the
<PAGE>

Registrable Securities or the initiation of any Proceedings for that purpose;
(iii) if at any time any of the representations and warranties of the Company
contained in this Agreement ceases to be true and correct in all material
respects; (iv) of the receipt by the Company of any notification with respect to
the suspension of the qualification or exemption from qualification of any of
the Registrable Securities for sale in any jurisdiction, or the initiation or
threatening of any Proceeding for such purpose; and (v) of the occurrence of any
event or passage of time that makes the financial statements included in the
registration statement or any prospectus constituting a portion thereof
ineligible for inclusion therein or any statement made in the Registration
Statement or prospectus or any document incorporated or deemed to be
incorporated therein by reference untrue in any material respect or that
requires any revisions to the registration statement or prospectus or other
documents so that, in the case of the registration statement and prospectus, it
will not contain any untrue statement of a material fact or omit to state any
material fact required to be stated therein or necessary to make the statements
therein, in light of the circumstances under which they were made, not
misleading.

     1.4  Furnish Information.  It will be a condition precedent to the
          -------------------
obligations of the Company to take any action pursuant to Section 1.2 hereof
                                                          -----------
that the selling Holders will furnish to the Company such information regarding
themselves, the Registrable Securities held by them, and the intended method of
disposition of such securities as will be required to effect the registration of
their Registrable Securities.

     1.5  Representations and Warranties of the Company.  The Company hereby
          ---------------------------------------------
makes the following representations and warranties to the Shareholders:

          (a)  Organization and Qualification.  The Company is a corporation
               ------------------------------
duly incorporated, validly existing and in good standing under the laws of the
State of California, with the requisite corporate power and authority to own and
use its properties and assets and to carry on its business as currently
conducted, except, however, where the failure to remain in good standing or to
carry on its business as currently conducted, as the case may be, could not,
individually or in the aggregate, (x) adversely affect the legality, validity or
enforceability of this Agreement or (y) adversely impair the Company's ability
to perform fully on a timely basis its obligations under this Agreement (any of
(x) or (y), a "Material Adverse Effect").

          (b)  Authorization; Enforcement.  The Company has the requisite
               --------------------------
corporate power and authority to enter into and to consummate the transactions
contemplated by this Agreement and otherwise to carry out its obligations
thereunder. The execution and delivery of this Agreement by the Company and the
consummation by it of the transactions contemplated thereby have been duly
authorized by all necessary action on the part of the Company and no further
action is required by the Company. This Agreement has been duly executed by the
Company and, when delivered in accordance with the terms of the Purchase
Agreement, will constitute the valid and binding obligation of the Company
enforceable against the Company in accordance with its terms.

          (c)  No Conflicts.  The execution, delivery and performance of this
               ------------
Agreement by the Company and the consummation by the Company of the transactions
contemplated thereby do not and will not (i) conflict with or violate any
provision of the Company's or any subsidiary's certificate or articles of
incorporation, bylaws or other charter documents (each as amended through the
date hereof), or (ii) subject to obtaining the Required Approvals (as defined
below), conflict with, or constitute a default (or an event which with notice or
lapse of time or both would become a default) under, or give to others any
rights of termination, amendment, acceleration or cancellation (with or without
notice, lapse of time or both) of, any agreement, credit facility, debt or other
instrument (evidencing a Company or subsidiary debt or otherwise) or other
understandings to which the Company or any subsidiary is a party or by which any
property or asset of the Company or any subsidiary is bound and affected, or
(iii) result in a violation of any law, rule, regulation, order, judgment,
injunction, decree or other restriction of any court or
<PAGE>

governmental authority to which the Company or a subsidiary is subject
(including federal and state securities laws and regulations), or by which any
property or asset of the Company or a subsidiary is bound or affected; except in
the case of each of clauses (ii) and (iii), as could not, individually or in the
aggregate, have or result in a Material Adverse Effect. The business of the
Company is not being conducted in violation of any law, ordinance or regulation
of any governmental authority, except for violations which, individually or in
the aggregate, could not have or result in a Material Adverse Effect.

          (d)  Filings, Consents and Approvals.  The Company is not required
               -------------------------------
to obtain any consent, waiver, authorization or order of, give any notice to, or
make any filing or registration with, any court or other federal, state, local
or other governmental authority or other Person in connection with the
execution, delivery and performance by the Company of this Agreement, other than
(i) the filing with the Commission of a registration statement covering the
resale of the Shares by the Purchasers and (ii) in all other cases where the
failure to obtain such consent, waiver, authorization or order, or to give such
notice or make such filing or registration could not have or result in,
individually or in the aggregate, a Material Adverse Effect (collectively, the
"Required Approvals").

          (e)  Form S-3 Eligibility.  The Company is eligible to register the
               --------------------
Shares for resale under Form S-3 promulgated under the Securities Act.

          (f)  Listing and Maintenance Requirements.  The Company has not, in
               ------------------------------------
the last six months preceding the date hereof received notice (written or oral)
from the Nasdaq, any stock exchange, market or trading facility on which the
Shares are or have been listed (or on which the Shares have been quoted) to the
effect that the Company is not in compliance with the listing or maintenance
requirements of such exchange, market or trading facility. The Company is, and
has no reason to believe that it will not in the foreseeable future continue to
be, in compliance with all such listing and maintenance requirements.

          (g)  Accuracy of SEC Documents.  The Company has timely filed, with
               -------------------------
the SEC under Sections 13 or 14(a) of the Securities Exchange Act of 1934, as
amended (the "Exchange Act"), since November 30, 1998 (such filed documents
being referred to collectively as the "SEC Documents"). As of their respective
filing dates, or such later date on which such reports were amended, the SEC
Documents complied in all material respects with the requirements of the
Exchange Act. The SEC Documents as of their respective dates, or such later date
on which such reports were amended, did not contain any untrue statement of a
material fact or omit to state a material fact required to be stated therein or
necessary to make the statements made therein, in light of the circumstances
under which they were made, not misleading. The financial statements included in
the SEC Documents (the "Financial Statements") comply as to form in all material
respects with applicable accounting requirements and with the published rules
and regulations of the SEC with respect thereto. Except as may be indicated in
the notes to the Financial Statements or, in the case of unaudited statements,
as permitted by Form 10-Q of the SEC, the Financial Statements have been
prepared in accordance with generally accepted accounting principles
consistently applied and fairly present the consolidated financial position of
the Company and any subsidiaries at the dates thereof and the consolidated
results of their operations and consolidated cash flows for the periods then
ended (subject, in the case of unaudited statements, to normal, recurring
adjustments).

     1.6  Indemnification.  In the event any Registrable Securities are included
          ---------------
in a registration statement under Section 1.2 hereof:
                                  -----------

          (a)  To the extent permitted by law, the Company will indemnify and
hold harmless each Holder, the partners, stockholders, officers and directors of
each Holder, any underwriter (as defined in the Securities Act) for such Holder
and each person, if any, who controls such Holder or underwriter
<PAGE>

within the meaning of the Securities Act or the Exchange Act against any losses,
claims, damages, or liabilities to which they may become jointly or severally
liable under the Securities Act, the Exchange Act or other federal or state
securities law, insofar as such losses, claims, damages, or liabilities (or
actions in respect thereof) arise out of or are based upon any of the following
statements, omissions or violations (collectively, a "Violation"):

               (1)  any untrue statement or alleged untrue statement of a
material fact contained in such registration statement, including any
preliminary prospectus or final prospectus contained therein or any amendments
or supplements thereto;

               (2)  the omission or alleged omission to state therein a material
fact required to be stated therein, or necessary to make the statements therein
not misleading; or

               (3)  any violation or alleged violation by the Company of the
Securities Act, the Exchange Act, any federal or state securities law or any
rule or regulation promulgated under the Securities Act, the Exchange Act or any
federal or state securities law in connection with the offering covered by such
registration statement; and the Company will reimburse each such Holder,
partner, stockholder, officer or director, underwriter or controlling person for
any legal or other expenses reasonably incurred by them, as incurred, in
connection with investigating or defending any such loss, claim, damage,
liability or action; provided however, that the indemnity agreement contained in
this Section 1.6(a) will not apply to amounts paid in settlement of any such
     --------------
loss, claim, damage, liability or action if such settlement is effected without
the consent of the Company (which consent will not be unreasonably withheld),
nor will the Company be liable in any such case for any such loss, claim,
damage, liability or action to the extent that it arises out of or is based upon
a Violation which occurs in reliance upon and in conformity with written
information furnished expressly for use in connection with such registration by
such Holder, partner, stockholder, officer, director, underwriter or controlling
person of such Holder (including, without limitation, Annex A).

          (b)  To the extent permitted by law, each selling Holder will
severally, but not jointly, indemnify and hold harmless the Company, each of its
directors, each of its officers who have signed the registration statement, each
person, if any, who controls the Company within the meaning of the Securities
Act, any underwriter and any other Holder selling securities under such
registration statement or any of such other Holder's partners, directors or
officers or stockholders or any person who controls such Holder within the
meaning of the Securities Act or the Exchange Act, against any losses, claims,
damages or liabilities (joint or several) to which the Company or any such
director, officer, controlling person, underwriter or other such Holder, partner
or director, officer, stockholder or controlling person of such other Holder may
become subject under the Securities Act, the Exchange Act or other federal or
state law, insofar as such losses, claims, damages or liabilities (or actions in
respect thereto) arise out of or are based upon any Violation that arises solely
as a result of written information furnished by such Holder expressly for use in
any registration statement or prospectus relating to the Shares or any amendment
or supplement thereto or any preliminary prospectus; and each such Holder will
reimburse any legal or other expenses reasonably incurred by the Company or any
such director, officer, controlling person, underwriter or other Holder,
partner, officer, director, stockholder or controlling person of such other
Holder in connection with investigating or defending any such loss, claim,
damage, liability or action; provided, however, that the indemnity agreement
contained in this Section 1.6(b) will not apply to amounts paid in settlement of
                  --------------
any such loss, claim, damage, liability or action if such settlement is effected
without the consent of the Holder, which consent will not be unreasonably
withheld; and provided further, that the total amounts payable in indemnity by a
Holder under this Section 1.6(b) in respect of any Violation will not exceed the
                  --------------
aggregate proceeds (net of discounts) received by such Holder upon the sale of
the Shares.
<PAGE>

          (c)  Promptly after receipt by an indemnified party under this Section
                                                                         -------
1.6 of notice of the commencement of any action (including any governmental
---
action), such indemnified party will, if a claim in respect thereof is to be
made against any indemnifying party under this Section 1.6, deliver to the
                                               -----------
indemnifying party a written notice of the commencement thereof and the
indemnifying party will have the right to participate in, and, to the extent the
indemnifying party so desires, jointly with any other indemnifying party
similarly noticed, to assume the defense thereof with counsel mutually
satisfactory to the parties; provided, however, that an indemnified party will
have the right to retain its own counsel, with the fees and expenses to be paid
by the indemnifying party, if representation of such indemnified party by the
counsel retained by the indemnifying party would be inappropriate due to actual
differing interests between such indemnified party and any other party
represented by such counsel in such proceeding. The failure to deliver written
notice to the indemnifying party within a reasonable time of the commencement of
any such action, if the indemnifying party is materially prejudiced thereby,
will relieve such indemnifying party of liability, but only to the extent that
such indemnifying party is prejudiced with respect to a specific claim.

          (d)  The foregoing indemnity agreement with respect to any prospectus
shall not inure to the benefit of any Holder or underwriter, or any person
controlling such Holder or underwriter, from whom the person asserting any
losses, claims, damages or liabilities purchased Registrable Securities, if a
copy of the prospectus (as then amended or supplemented if the Company shall
have furnished any amendments or supplements thereto) provided by the Company
was not sent or given by or on behalf of such Holder or underwriter to such
person, if required by law so to have been delivered, at or prior to the written
confirmation of the sale of the Registrable Securities to such person, and if
the prospectus (as so amended or supplemented) would have cured the defect
giving rise to such loss, claim, damage or liability.

          (e)  If the indemnification provided for in Section 1.6(a) or 1.6(b)
                                                      --------------    ------
hereof shall be unavailable to hold harmless an indemnified party in respect of
any liability under the Securities Act, then, and in each such case, the
indemnifying party, in lieu of indemnifying such indemnified party hereunder,
shall contribute to the amount paid or payable by such indemnified party as a
result of such loss, liability, claim, damage or expense in such proportion as
is appropriate to reflect the relative fault of the indemnifying party on the
one hand and of the indemnified party on the other in connection with the
statement or omissions that resulted in such loss, liability, claim, damage or
expense as well as any other relevant equitable considerations. The relative
fault of the indemnifying party and of the indemnified party shall be determined
by reference to, among other things, whether the untrue or alleged untrue
statement of a material fact or the omission to state a material fact relates to
information supplied by the indemnifying party or by the indemnified party and
the parties' relative intent, knowledge, access to information and opportunity
to correct or prevent such statement or omission; provided that each Holder's
obligation to contribute pursuant to this subsection (e) is several in the
proportion that the proceeds of the offering received by such Holder bears to
the total proceeds of the offering received by all holders and not joint. No
person or entity guilty of fraudulent misrepresentation (within the meaning of
Section 11(f) of the Securities Act) will be entitled to contribution from any
person or entity who was not guilty of such fraudulent misrepresentation.

          (f)  The obligations of the Company and Holders under this Section 1.6
                                                                     -----------
will survive the completion of any offering of Registrable Securities in a
registration statement, and otherwise.

     1.7  Rule 144 Reporting.  With a view to making available the benefits of
          ------------------
certain rules and regulations of the Commission which may at any time permit the
sale of the Registrable Securities to the public without registration, while a
public market exists for the Common Stock of the Company, the Company will:
<PAGE>

          (a)  Make and keep public information available, as those terms are
understood and defined in Rule 144 under the Securities Act, at all times while
the Company is reporting under the Exchange Act;

          (b)  Use its Best Efforts to file with the SEC in a timely manner all
reports and other documents required of the Company under the Securities Act and
the Exchange Act (at any time it is subject to such reporting requirements); and

          (c)  So long as a Holder owns any Registrable Securities, furnish to
the Holder forthwith upon request a written statement by the Company as to its
compliance with the reporting requirements of Rule 144, and of the Securities
Act and the Exchange Act (at any time it is subject to the reporting
requirements of the Exchange Act), a copy of the most recent annual or quarterly
report of the Company, and such other reports and documents of the Company as a
Holder may reasonably request in availing itself of any rule or regulation of
the SEC allowing a Holder to sell any such securities without registration (at
any time the Company is subject to the reporting requirements of the Exchange
Act).

     1.8  Blocking Notice.  For a period not exceeding either (i) twenty (20)
          ---------------
consecutive Business Days or (ii) an aggregate of thirty (30) Business Days in
any twelve (12) month period, the Company may suspend the ability of the Holders
to make dispositions under the registration statement or prospectus by providing
the Holders with written notice (a "Blocking Notice") if the Company's Board of
Directors determines in its good faith judgment that the Company's obligation to
ensure that such registration statement and prospectus contain current and
complete information would require the Company to make a public disclosure
regarding a material non-public transaction, provided, that the Company shall
not be entitled to deliver a Blocking Notice within ten (10) Business Days of
the expiration of any Blocking Notice previously delivered. Each Blocking Notice
shall contain a general statement of the reasons for such postponement and an
approximation of the anticipated delay. Notwithstanding anything to the contrary
herein, in the event of a merger of the Company with or into another entity that
is not wholly-owned by the Company and is reportable, if consummated, under Item
2 of Form 8-K under the Exchange Act, the Company may deliver a Blocking Notice
for a period of up to sixty (60) consecutive Business Days in any twelve (12)
month period, in which case, the number of consecutive Business Days available
to the Company pursuant to clause (ii) of this Section shall be reduced by such
number of Business Days. Each Holder agrees by acquisition of the Registrable
Securities that, upon receipt of a Blocking Notice from the Company, such Holder
shall not dispose of, sell or offer for sale the Registrable Securities pursuant
to the registration statement until such Holder receives (i) copies of the
supplemented or amended prospectus, or until counsel for the Company shall have
determined that such disclosure is not required due to subsequent events, (ii)
notice in writing from the Company that the use of the prospectus may be resumed
and (iii) copies of any additional or supplemental filings that are incorporated
by reference to in the prospectus. In the event the Company shall provide any
Blocking Notice pursuant to this Section, the period during which the Company is
required to keep the registration statement (filed pursuant to Section 1.2)
effective shall be extended for the amount of time equal to the number of days
during which such Blocking Notice is in effect.

     1.9  Holder Information.  Each Holder covenants that it will promptly
          ------------------
notify the Company of any changes in the information set forth in the
registration statement regarding such Holder or the information contained on
Annex A.

2.   Miscellaneous.
     -------------

     2.1  Termination of the Company's Obligations.  The Company shall have no
          ----------------------------------------
obligations to register or maintain any registration statement governing
Registrable Shares and no penalties or damages will accrue or be payable as a
result of such failure to register or maintain any registration statement, (a)
if
<PAGE>

all Registrable Shares have been registered and sold pursuant to a registration
statement effected pursuant to this Agreement, or (b) at such time as all
Registrable Shares held by Shareholders may be sold under Rule 144(k), as it may
be amended from time to time, including but not limited to amendments that
reduce that period of time that securities must be held before such securities
may be sold pursuant to such Rule.

     2.2  Successors and Assigns.  This Agreement shall inure to the benefit of
          ----------------------
and be binding upon the successors and assigns of each of the parties hereto
including any person to whom Registrable Shares are transferred in accordance
with the provisions of the Purchase Agreement.

     2.3  Amendment and Waivers.  Except as otherwise provided herein, the
          ---------------------
provisions of this Agreement may not be amended, modified or supplemented, and
waivers or consents to departure from the provisions hereof may not be given
unless agreed upon in writing by the Company and the holders of a majority of
the Registrable Shares.

     2.4  Notices.  Any and all notices or other communications or deliveries
          -------
required or permitted to be provided hereunder shall be in writing and shall be
deemed given and effective on the earliest of (i) the date of transmission, if
such notice or communication is delivered via facsimile at the facsimile
telephone number specified in this Section prior to 6:30 p.m. (San Diego time)
on a Business Day (with confirmation of transmission), (ii) the Business Day
after the date of transmission, if such notice or communication is delivered via
facsimile at the facsimile telephone number specified in this Agreement later
than 6:30 p.m. (San Diego time) on any date and earlier than 11:59 p.m. (San
Diego time) on such date (with confirmation of transmission), (iii) the Business
Day following the date of mailing, if sent by nationally recognized overnight
courier service, or (iv) upon actual receipt by the party to whom such notice is
required to be given. The address for such notices and communications shall be
as follows:

          (a)  If to the Company:

               CardioDynamics International Corp.
               6175 Nancy Ridge Drive, Suite 300
               San Diego, CA 92121
               Attention:  Chief Financial Officer
               ---------
               Telecopy:   (858) 623-8415
               --------

               with a copy to:

               Pillsbury Winthrop LLP
               101 West Broadway, Suite 1800
               San Diego, CA 92101
               Attention:  David R. Snyder, Esq.
               ---------
               Telecopy:   (619) 236-1995
               --------

          (b)  If to a Shareholder, at the address set forth below such
Shareholder's name on the signature page hereof.

     2.5  Headings.  The table of contents and section headings contained in
          --------
this Agreement are for reference purposes only and shall not be deemed a part of
this Agreement or affect in any way the meaning or interpretation of this
Agreement.

     2.6  Construction.  The parties have participated jointly in the
          ------------
negotiation and drafting of this Agreement. In the event an ambiguity or
question of intent or interpretation arises, this Agreement shall
<PAGE>

be construed as if drafted jointly by the parties and no presumption or burden
of proof shall arise favoring or disfavoring any party by virtue of the
authorship of any of the provisions of this Agreement.

     2.7  Entire Agreement.  This Agreement constitutes the entire agreement
          ----------------
among the parties with respect to the subject matter hereof and supersede all
prior negotiations, agreements and understandings of the parties of any nature,
whether oral or written, relating thereto.

     2.8  Governing Law.  All questions concerning the construction, validity,
          -------------
enforcement and interpretation of this Agreement shall be governed by and
construed and enforced in accordance with the internal laws of the State of
California, without regard to the principles of conflicts of law thereof. Each
party agrees that all legal proceedings concerning the interpretations,
enforcement and defense of the transactions contemplated by this Agreement
(whether brought against a party hereto or its respective affiliates, directors,
officers, shareholders, employees or agents) shall be commenced in the state and
federal courts sitting in the San Diego, California (the "California Courts").
Each party hereto hereby irrevocably submits to the exclusive jurisdiction of
the California Courts for the adjudication of any dispute hereunder or in
connection herewith or with any transaction contemplated hereby or discussed
herein (including with respect to the enforcement of this Agreement), and hereby
irrevocably waives, and agrees not to assert in any suit, action or proceeding,
any claim that is not personally subject to the jurisdiction of any such court,
that such suit, action or proceeding is improper or that such California Courts
are inconvenient or will be an improper form for such proceeding. Each party
hereto (including its affiliates, agents, officers, directors and employees)
hereby irrevocably waives personal service of process and consents to process
being served in any such suit, action or proceeding by mailing a copy thereof
via registered or certified mail or overnight delivery (with evidence of
delivery) to such party at the address in effect for notices to it under this
Agreement and agrees that such service shall constitute good and sufficient
service of process and notice thereof. Nothing contained herein shall be deemed
to limit in any way any right to serve process in any manner permitted by law.
Each party hereto (including its affiliates, agents, officers, directors and
employees) hereby irrevocably waives, to the fullest extent permitted by
applicable law, any and all right to trial by jury in any legal proceeding
arising out of or relating to this Agreement or the transactions contemplated
hereby. If either party shall commence an action or proceeding to enforce any
provisions of this Agreement, then the prevailing party in such action or
proceeding shall be reimbursed by the other party for its attorneys fees and
other costs and expenses incurred with the investigation, preparation and
prosecution of such action or proceeding.

     2.9  Counterparts.  This Agreement may be executed in any number of
          ------------
counterparts, each of which shall be deemed an original but all of which
together will constitute one and the same instrument.

     2.10 Compliance.  Each Holder covenants and agrees that it will comply with
          ----------
the prospectus delivery requirements of the Securities Act as applicable to it
in connection with sales of Registrable Securities pursuant to the registration
statement
<PAGE>

     IN WITNESS WHEREOF, the parties hereto have caused this Registration Rights
Agreement to be executed as of the date first above written.

THE COMPANY:                         CardioDynamics International Corporation, a
                                     California corporation

                                     By:      /s/ Michael K. Perry
                                              --------------------------------
                                     Name:    Michael K. Perry
                                     Title:   Chief Executive Officer
<PAGE>

THE SHAREHOLDERS:
                              /s/ Lester B. Knight
                              -------------------------------------------
                              Lester B. Knight

                              Shares:  250,000

                                 Address:  Lester B. Knight
                                           c/o RoundTable Healthcare Partners
                                           272 E. Deerpath Road, Suite 350
                                           Lake Forest, IL  60045
                                           Facsimile No.: 847-482-9215

                              With a copy to:

                                           Tony Decello
                                           c/o McCormack Advisors International
                                           IMG Center, Suite 100, 1360 East 9th
                                           Cleveland, OH  44114
                                           Facsimile No.: 216-436-3396

                                           Robyn Schneider
                                           c/o Prairie Capital Management
                                           920 York Road, Suite 350
                                           Hinsdale, IL  60521
                                           Facsimile No.: 630-850-9951

               [Signature Page to Registration Rights Agreement]
<PAGE>

                              /s/ Joseph F. Damico
                              -------------------------------------------
                              Joseph F. Damico

                              Shares:      100,000

                                 Address:  1388 W. Lake Street
                                           Libertyville, IL 60048
                                           Facsimile No.: 847-482-9215

                              With a copy to:

                                           Tony Decello
                                           c/o McCormack Advisors International
                                           IMG Center, Suite 100, 1360 East 9th
                                           Cleveland, OH  44114
                                           Facsimile No.: 216-436-3396

               [Signature Page to Registration Rights Agreement]
<PAGE>

                              /s/ Jack L. McGinley
                              -------------------------------------------
                              Jack L. McGinley

                              Shares:      100,000

                                 Address:  Jack L. McGinley
                                           c/o RoundTable Healthcare Partners
                                           272 E. Deerpath Road, Suite 350
                                           Lake Forest, IL 60045
                                           Facsimile No.: 847-482-9215

                              With a copy to:

                                           Tom Zanecchia
                                           c/o Wealth Management Consultants
                                           475 17th Street, Suite 570
                                           Denver, CO  80202
                                           Facsimile No.: 303-292-9226

                                           Chuck Martin
                                           Benham, Ichen & Knox LLP
                                           1117 South Milwaukee Ave., Suite C11
                                           Libertyville, IL  60048-3763
                                           Facsimile No.:  847-362-5016

               [Signature Page to Registration Rights Agreement]
<PAGE>

                              /s/ Thomas Fogarty
                              -------------------------------------------
                              Thomas Fogarty, MD

                              Shares:      35,000

                                 Address:  3270 Alpine Road
                                           Portola Valley, CA 94028

              [Signature Page to Registration Rights Agreement]
<PAGE>

                              /s/ Todd E. Warnock
                              -------------------------------------------
                              Todd E. Warnock

                              Shares:      25,000

                                 Address:  739 Lincoln Avenue
                                           Winnetka, IL  60093
                                           Facsimile No.: 847-446-4339

               [Signature Page to Registration Rights Agreement]<PAGE>

                                                                     EXHIBIT 4.3
                                                                     -----------

                   CardioDynamics International Corporation
                       6175 Nancy Ridge Drive, Suite 300
                              San Diego, CA 92121

                                August 13, 2001

The Allen E. Paulson Living Trust
c/o Paulson Enterprises
P.O. box 9660
Rancho Santa Fe, California 92067
Attention:  J. Michael Paulson and Edward White

Ladies and Gentlemen:

Reference is made to a certain Securities Purchase Agreement dated as of August
13, 2001 (the "Purchase Agreement"), pursuant to which the Trust has agreed to
sell (the "Sale") up to five hundred ten thousand (510,000) shares of
CardioDynamics International Corporation (the "Company") Common Stock (the
"Shares") to certain purchasers identified in the Purchase Agreement (the
"Purchasers").

As contemplated by the Purchase Agreement, the Company will enter into a
Registration Rights Agreement dated as of the date of the Purchase Agreement
(the "Rights Agreement") with the Purchasers, whereby the Company will agree to
register the Shares for resale and keep such registration statement effective
for a period of two (2) years, as more fully described in the Rights Agreement.
The Company hereby agrees to use its best efforts to cause such registration
statement to be declared effective within 90 days following the Closing Date as
such term is defined in the Purchase Agreement.  The Trust hereby agrees to
reimburse the Company, out of escrow established in connection with the Purchase
Agreement (if any), for all of the Company's expenses (up to a maximum of
$10,000 in the aggregate) that the Company incurs in connection with any
registration, qualification and compliance requested pursuant to the Rights
Agreement, including without limitation, all filing, registration and
qualification, and accounting fees and the fees and disbursements of its
counsel.

Further, as compensation for (i) our introduction of the Purchasers to the
Trust, (ii) fees and expenses we incurred in connection with such introduction,
and (iii) the otherwise unreimbursed fees and expenses related to the
registration of the Shares as well as the devotion of management time to and
opportunity cost associated with preparation and review of the documents
associated with the Sale and the registration and qualification of the Shares,
the Trust hereby agrees to pay to the Company, in cash one-half at the time of
the Settlement Date of the Sale as set forth in the Purchase Agreement and one-
half at the time the registration statement with respect to such Shares is
declared effective, a fee equal to three and one-half percent (3 1/2%) of the
gross purchase price paid by the Purchasers for the Shares.
<PAGE>

Please execute and return this letter agreement (which may be executed in
counterparts) to the undersigned to concur that (i) this sets forth the Trust's
complete and entire understanding with regards to the subjects described within,
and (ii) that this letter agreement may not be amended or modified except in a
writing executed on behalf of both the Company and the Trust.  By execution
hereof, we both further agree that this letter agreement is to be governed by
and construed in accordance with the laws of the State of California, as applied
to contracts among California residents, made and to be performed entirely
within the State of California.

                                    CardioDynamics International Corporation
                                    a California corporation

                                    By: /s/Michael K. Perry
                                        ------------------------------------
                                        Name:  Michael K. Perry
                                        Title:  Chief Executive Officer

Accepted and agreed as of August 13, 2001:
The Allen E. Paulson Living Trust

By: /s/ J. Michael Paulson
    ----------------------------------------
    Name:  J. Michael Paulson, Co-Trustee

By: /s/ Edward White
    ----------------------------------------
    Name: Edward White, Co-Trustee

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