Document:

<PAGE>

                                                                     EXHIBIT 4.2

   THIS SENIOR SECURED PROMISSORY NOTE ("NOTE") IS SUBJECT TO THE TERMS OF AN
 INDENTURE DATED ______________ ___, 2001 (AS AMENDED OR SUPPLEMENTED FROM TIME
 TO TIME, THE "INDENTURE") BETWEEN CARDIAC SCIENCE, INC. AND BNY WESTERN TRUST
COMPANY, AS TRUSTEE (THE "TRUSTEE"). THE TERMS OF THIS NOTE INCLUDE THOSE STATED
IN THE INDENTURE AND THOSE MADE PART OF THE INDENTURE BY REFERENCE TO THE TRUST
         INDENTURE ACT OF 1939, AS AMENDED (THE "TRUST INDENTURE ACT").

THIS INSTRUMENT IS REGISTERED AS TO BOTH PRINCIPAL AND INTEREST WITH THE ISSUER
AND TRANSFER HEREOF MAY BE EFFECTED ONLY BY THE SURRENDER OF THE OLD INSTRUMENT
AND THE ISSUANCE OF A NEW INSTRUMENT BY THE ISSUER TO THE NEW HOLDER. THE HOLDER
HEREOF IS HEREBY NOTIFIED THAT THIS INSTRUMENT IS NOT LISTED NOR IS IT TRADABLE
                     ON ANY ESTABLISHED SECURITIES MARKET.

                    [FORM OF] SENIOR SECURED PROMISSORY NOTE

$_____________________________                    ISSUE DATE: ___________, 2001

    FOR VALUE RECEIVED and pursuant to that certain Second Amended and Restated
Agreement and Plan of Merger dated as of August 3, 2001 (the "APM") by and among
Cardiac Science, Inc., a Delaware corporation ("Cardiac"), Cardiac Science
Acquisition Corp., a Minnesota corporation (a wholly owned subsidiary of
Cardiac, "Merger Sub"), and Survivalink Corporation, a Minnesota corporation
("Survivalink"), the undersigned, Cardiac (the "Issuer") hereby promises to pay
to the order of ________________________ (the "Holder") or the assigns of
Holder, the sum of __________________________ _______________ plus accrued
interest as provided below.

    This Note has the following terms:

Maturity:               Eighteen (18) months from date of issue, subject to an
                        automatic six (6) month extension upon payment of a one-
                        time extension fee to the Holder (discussed below).

Interest Rate:          Ten percent (10.00%) simple interest per annum, fixed
                        rate.

Interest Payment Date:  Accrued and unpaid interest will be paid on the maturity
                        date.

Payment of Principal:   The outstanding  principal will be paid on the maturity
                        date.

Extension Fee:          In the event that Issuer elects to extend the term of
                        the Note for a period not to exceed six (6) months, the
                        Issuer shall pay a one-time extension fee to the Holder
                        in an amount equal to five percent (5%) of the
                        outstanding principal and accrued and unpaid interest at
                        the time of extension.

Ranking:                Senior to the Issuer's outstanding indebtedness.

Security:               Blanket security interest in the Issuer's assets.
<PAGE>

Optional Prepayment:    This Note and any accrued interest may be prepaid in
                        whole or in part at any time without penalty.

Mandatory Prepayment:   In the event that the Issuer raises additional capital
                        in excess of fifteen million dollars ($45,000,000)
                        whether through an equity or debt financing, ninety-
                        three percent (93%) of such additional capital shall be
                        used to redeem this Note and any accrued and unpaid
                        interest.

    All payments shall be made in lawful money of the United States to the
registered holder of this Note in accordance with the provisions of the
Indenture.

    The following are events of default under the Indenture: (a) the Issuer's
failure to pay or perform any obligation, liability or indebtedness of the
Issuer to the Holder under this Note as and when due (whether upon demand, at
maturity or by acceleration, and subject to the terms of this Note, the
Indenture and the APM); (b) the commencement of a proceeding by or against the
Issuer for dissolution (other than administrative dissolution where prompt re-
instatement efforts are initiated and followed through to completion), which
proceeding is not discharged within thirty (30) days after such commencement;
(c) the insolvency of the Issuer; (d) the appointment of a custodian, trustee,
liquidator or receiver for a material portion of the property of the Issuer,
which trustee is not discharged within thirty (30) days after such appointment;
(e) an assignment for the benefit of creditors of a material portion of the
property of the Issuer; or (f) the filing of a petition under bankruptcy,
insolvency or debtor's relief law or the filing of a petition for any adjustment
of indebtedness, composition or extension by or against the Issuer, which
petition is not discharged within thirty (30) days after such filing. Whenever
there is a default under this Note, the entire balance outstanding hereunder
(however acquired or evidenced) shall, at the option of the Trustee, or as
otherwise provided in the Indenture, become immediately due and payable in
accordance with the Indenture. Additionally, the Holder shall have all rights
and remedies available under the APM and the Indenture.

     The Issuer hereby waives presentment, protest and demand, notice of
protest, demand and dishonor and nonpayment of this Note, agrees to pay all
reasonable costs of collection when incurred (including without limitation
reasonable attorneys' fees), and agrees to perform and comply with each of the
covenants, agreements, conditions, provisions and agreements of the Issuer
contained in each and every instrument evidencing or securing said indebtedness.
The Issuer agrees that its liabilities under this Note are absolute and
unconditional without regard to the liability of any other party.  The Issuer
hereby waives the right to interpose any set-off, counterclaim, or defense or
any nature or description whatsoever in connection with any Holder's enforcement
of its rights under this Note.

    This Note is subject to all of the terms of the Indenture and the Trust
Indenture Act, and holders of the Notes are referred to the Indenture and such
Act for a statement of the respective rights, limitations of rights, duties and
immunities thereunder of the Issuer, the Trustee and each Holder and of the
terms upon which the Notes are, and are to be, authenticated and delivered. The
terms of this Note contained herein do not purport to be complete and are
qualified by reference to the Indenture. To the extent permitted by applicable
law, in the event of any inconsistency between the terms of this Note and the
terms of the Indenture, the terms of the Indenture shall control.

    This Note shall not be valid until the Trustee or an authenticating agent
manually signs the certificate of authentication on this Note.
<PAGE>

    IN WITNESS WHEREOF, the Issuer executes this Note effective on the ____ day
of _____________, 2001.

                             CARDIAC SCIENCE, INC.

                             [DRAFT]___________________________
                              -----

                              By:__________________, __________

Attest: _________________________

        ______________, Secretary

                    TRUSTEE'S CERTIFICATE OF AUTHENTICATION

     BNY Western Trust Company, as Trustee, certifies that this is one of the
Notes referred to in the Indenture.

        By:[DRAFT]_____________________________________
           -------
           Authorized Signatory<PAGE>

                                                                   Exhibit 10.17

                            SHAREHOLDERS AGREEMENT

     This Shareholders Agreement ("Agreement") is entered into as of __________
                                   ---------
__, 2001, by and among Cardiac Science, Inc., a Delaware corporation (the
"Company"), and the former shareholders of Survivalink or former holders of
--------
options or warrants to purchase shares of capital stock of Survivalink, each
listed on the Shareholder Signature Page attached hereto (collectively, the
"Shareholders").
-------------

     WHEREAS, the Board of Directors of the Company and Survivalink Corporation,
a Minnesota corporation ("Survivalink") deem it in the best interests of their
                          -----------
respective companies and their respective shareholders to enter into that
certain First Amended and Restated Agreement and Plan of Merger, dated as of
June 5, 2001 (the "Merger Agreement"), pursuant to which the Company will
                   ----------------
acquire all the outstanding securities of Survivalink (the "Merger") and, in
                                                            ------
furtherance thereof, have approved the Merger and the transactions set forth in
the Merger Agreement;

     WHEREAS, pursuant to the Merger Agreement, the Company will deliver to the
Shareholders the merger consideration consisting of cash, secured promissory
notes of the Company (the "Notes") and shares of its common stock, $0.001 par
value per share ("Common Stock," or "Merger Shares," and collectively with the
cash and notes, the "Merger Consideration");

     WHEREAS, in connection with the Merger, Common Stock and Notes equal to
five percent (5%) of the Merger Consideration shall be held in escrow by the
Escrow Agent, pursuant to the terms of the Escrow Agreement, by and among the
Company, the Escrow Agent, and the Shareholders' Representative (the "Escrow
Agreement"); and,

     WHEREAS, the parties hereto desire to enter into this Agreement to evidence
the foregoing agreement of the Company and the mutual covenants of the parties
relating thereto.

     NOW THEREFORE, in consideration of the mutual agreements, covenants and
conditions contained herein, the Company and the Shareholders hereby agree as
follows:

     1. Representations and Warranties of the Shareholders. This Agreement and
the Merger Agreement is made with the Shareholders in reliance upon each
Shareholder's representations to the Company, which by the Shareholder's
execution of this Agreement, each such Shareholder hereby severally warrants and
represents that:

        1.1 Title to Capital Stock. Each Shareholder represents that it holds
good and marketable title to his, her or its shares of capital stock of
Survivalink, free and clear of all liens, agreements, voting trusts, proxies and
other arrangements or restrictions of any kind whatsoever, other than as
disclosed in the Merger Agreement.

        1.2 No Restrictions. There are no limitations or restrictions on the
Shareholder's ability to invest in the Company and to perform its obligations
under this Agreement.

        1.3 Termination of Warrants. Each Shareholder hereby acknowledges and
agrees that any warrant that they may hold as of the Effective Time of the
Merger that was originally issued by Survivalink and that entitles the holder
thereof to purchase equity securities of Survivalink
<PAGE>

is or will be automatically cancelled by reason of the Merger and that all
applicable notices and provisions called for by the terms of such warrant have
either been duly made or are hereby waived by such Shareholder and the
Shareholder agrees to surrender and deliver the original copy of such warrant to
Survivalink within a reasonable amount of time after the Effective Time.

     2.  LOCK-UP

         2.1 Lock-up/Further Restrictions on Transfer. Each Shareholder hereby
agrees that it shall not sell, transfer, assign, convey, donate, pledge,
encumber, alienate or in any way dispose of their Registrable Shares (any one of
the foregoing, a "Transfer"), except in accordance with the following schedule:
                  --------
<TABLE>
<CAPTION>
Number of Days after Effective Time, after         Maximum Percentage of Transferable
which Registrable Shares are Transferable          Registrable Shares (cumulative)
-------------------------------------------------------------------------------------
<S>                                                <C>
            after 90 days                                             34%
-------------------------------------------------------------------------------------
            after 180 days                                            67%
-------------------------------------------------------------------------------------
            after 270 days                                           100%
-------------------------------------------------------------------------------------
</TABLE>

provided that, each Shareholder may Transfer Registrable Shares in a non-public
-------------
transaction, notwithstanding this Section 3.9, to any person if such person
                                  -----------
agrees to join and be bound by the terms of this Agreement.  Any purported or
attempted Transfer whether voluntary or involuntary, in violation of this

Section 3.9 shall be null and void  and of no legal effect.
-----------

     2.2 Stop Transfer Instructions; No Requirement to Transfer. Each
Shareholder agrees that, in order to ensure compliance with the restrictions
referred to herein, the Company may issue appropriate "stop transfer"
instructions to its transfer agent. The Company shall not be required (i) to
transfer or have transferred on its books any shares of Common Stock that have
been sold or otherwise transferred in violation of any of the provisions of this
Agreement or the Merger Agreement or (ii) to treat as owner of such shares of
Common Stock or to accord the right to vote or pay dividends to any purchaser or
other transferee to whom such shares of Common Stock shall have been so
transferred in violation of any provision of this Agreement or the Merger
Agreement.

     2.3 Legends. Each Shareholder understands and agrees that there will be
placed on the certificates evidencing the ownership of the Registrable Shares
the following legends, in addition to any legends required by applicable
securities laws, by the Company's certificate of incorporation, as amended from
time to time, until such time as such legends or portions thereof are no longer
required in contemplation of the provisions of this Agreement, the Merger
Agreement or the Securities Act:

          THE SECURITIES REPRESENTED BY THIS CERTIFICATE MAY NOT BE OFFERED,
     SOLD, PLEDGED, EXCHANGED, TRANSFERRED OR OTHERWISE DISPOSED OF EXCEPT IN
     ACCORDANCE WITH THE REQUIREMENTS OF THE SECURITIES ACT OF 1933, AS AMENDED
     (THE "SECURITIES ACT").  THE SECURITIES MAY NOT BE OFFERED, SOLD, PLEDGED,
     EXCHANGED OR TRANSFERRED UNLESS (1) A REGISTRATION STATEMENT UNDER THE
     SECURITIES ACT (AND CURRENT PROSPECTUS) IS IN EFFECT AS TO THE SECURITIES,
     OR (2) AN

                                       2
<PAGE>

     EXEMPTION FROM REGISTRATION IS AVAILABLE, OR (3) THE SECURITIES ARE SOLD
     PURSUANT TO RULE 144 OF THE SECURITIES ACT. THE ISSUER OF THESE SECURITIES
     MAY REQUIRE AN OPINION OF COUNSEL IN FORM AND SUBSTANCE SATISFACTORY TO THE
     ISSUER TO THE EFFECT THAT ANY PROPOSED TRANSFER OR RESALE IS IN COMPLIANCE
     WITH THE SECURITIES ACT AND ANY APPLICABLE STATE OR OTHER NATIONAL
     SECURITIES LAWS.

     THE HOLDER OF THESE SECURITIES HAS AGREED PURSUANT TO THE TERMS OF A
     SHAREHOLDERS AGREEMENT (A COPY OF WHICH IS AVAILABLE UPON REQUEST OF THE
     COMPANY) NOT TO TRANSFER THE SAME UNTIL A CERTAIN DATE.

         Any legend required by applicable state securities the laws.

     3.  Shareholders' Representative.  Each Shareholder hereby acknowledges the
appointment of a committee consisting of a representative of U.S. Trust, a
representative of Fidelity Investments and Mark Wagner as the Shareholders'
Representative (as defined in the Merger Agreement) pursuant to Section 9.06 of
the Merger Agreement and hereby grants to the Shareholders' Representative the
authority to act on its behalf in accordance with Section 9.06 of the Merger
Agreement, including, without limitation, the authority to act on behalf of the
Shareholders in connection with payments made out of the Escrow Account pursuant
to the terms of the Merger Agreement and the Escrow Agreement.  Notwithstanding
the foregoing, each shareholder shall indemnify the Shareholders' Representative
for all actions taken on behalf of the Shareholders and in accordance with the
authority granted herein; provided, however, that the maximum amount of the
indemnification obligation for each Shareholder shall not exceed the value of
the proceeds received by such Shareholder in the Merger.

     4.  Assignability.  This Agreement shall be binding upon and inure to the
benefit of the permitted heirs, successors and assigns of the parties hereto,
but any purported assignment or transfer is subject to the terms of this
Agreement, including but not limited to, Section 2.1.
                                         -----------

     5.  Governing Law.  This Agreement shall be governed by and construed in
accordance with the laws of the State of Delaware.

     6.  Amendment.  Any modification, amendment, or waiver of this Agreement or
any provision hereof, either retroactively or prospectively, shall be in writing
and executed by the Company and the holders of not less than fifty percent (50%)
of the Merger Shares which shall be binding upon all of the parties hereto.

     7.  Counterparts.  This Agreement may be executed in any number of
counterparts, each of which will be an original as regards any party whose
signature appears thereon and all of which together will constitute one and the
same instrument. This Agreement will become binding when one or more
counterparts hereof, individually or taken, will bear the signatures of both
parties reflected hereon as signatories.

     8.  Notice.  Any notices and other communications required or permitted
under this Agreement shall be effective if in writing and delivered personally
or sent by telecopier, federal express or registered or certified mail, postage
prepaid, addressed as follows:

                                       3
<PAGE>

          If to the Shareholders: The names and addresses set forth on Exhibit A
hereto.

                    with a copy to:
                    --------------

                    Dorsey & Whitney LLP
                    Pillsbury Center South
                    220 South Sixth Street
                    Minneapolis, MN 55402
                    Telecopy:  (612) 340-8827
                    Attention:  Michael J. McDonnell

          If to the Company:

                    Cardiac Science, Inc.
                    16931 Millikan Ave.
                    Irvine, CA  92606
                    Telecopy:  (949) 951-7315
                    Attention:  Raymond Cohen

                    with a copy to:
                    --------------

                    Stradling Yocca Carlson & Rauth
                    660 Newport Center Drive, Suite 1600
                    Newport Beach, CA  92660
                    Telecopy:  (949) 725-4100
                    Attention:  Shivbir S. Grewal

     Unless otherwise specified herein, such notices or other communications
shall be deemed effective (a) on the date delivered, if delivered personally,
(b) two business days after being sent, if sent by Federal Express, (c) one
business day after being sent, if sent by telecopier with confirmation of good
transmission and receipt, and (d) three business days after being sent, if sent
by registered or certified mail.  Each of the parties herewith shall be entitled
to specify another address by giving notice as aforesaid to each of the other
parties hereto.

     9.  Stamp Duty.  Any stamp duty, transfer tax or similar tax payable in
connection with the transfer of by any Shareholder of its Survivalink securities
shall be payable by such Shareholder.

                           (signature pages follow)

                                       4
<PAGE>

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

                              Cardiac Science, Inc., a Delaware corporation

                              _______________________________________________
                              By:  Raymond Cohen
                              Its: President

                                       5
<PAGE>

                        SHAREHOLDER  SIGNATURE PAGE TO

                          THE SHAREHOLDERS AGREEMENT

 This page constitutes an executed counterpart, which, when taken together with
   all other counterparts, shall constitute one originally executed document.

     More than one signature block is provided below for convenience purposes
     ------------------------------------------------------------------------
     for those shareholders who hold title to their Survivalink stock jointly,
     or otherwise if more than one shareholder wishes to sign on the same page
     for any reason such as because  they are in close proximity with one
     another or are affiliated companies.

     IN WITNESS WHEREOF, the undersigned shareholders have executed this
Shareholders Agreement as of the date first written above.

<TABLE>
<CAPTION>
SHAREHOLDER                                          SHAREHOLDER
<S>                                                  <C>

_________________________________________________    _________________________________________________

_________________________________________________    _________________________________________________
(Print name of person/company on lines above)        (Print name of person/company on lines above)

_________________________________________________    _________________________________________________
(signature)                                          (signature)

_________________________________________________    _________________________________________________
(Title of officer/partner/manager, if applicable)    (Title of officer/partner/manager, if applicable)

_____________________________________________        _______________________________________________
(Print name of officer/partner/manager)              (Print name of officer/partner/manager)

Address: _______________________                     Address: _______________________
         _______________________                              _______________________
         _______________________                              _______________________
</TABLE>

                                       6

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