Document:

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                                                                  EXHIBIT 10.2.3

                             ARCH CAPITAL GROUP LTD.

                      AMENDMENT TO STOCK OPTION AGREEMENTS

        WHEREAS, Arch Capital Group Ltd. (the "Company"), a Delaware
corporation, has granted to Robert Clements (the "Option Holder") the options to
purchase common stock, $0.01 par value per share, of the Company set forth on
SCHEDULE I hereto (the "Options") under the Company's 1995 and/or 1999 Long Term
Incentive and Share Award Plans;

        NOW, THEREFORE, the parties have agreed to amend the Options as follows:

        The definition of "Change in Control" included in Paragraph (f) of each
Option shall be amended and restated in its entirety as follows:

            "Change in Control" means any of the following occurring after
      the date hereof:

               a. any person (within the meaning of the Securities Exchange Act
            of 1934, as amended (the "Exchange Act")), other than a Permitted
            Person or an Initial Investor, is or becomes the "beneficial owner"
            (as defined in Rule 13d-3 under the Exchange Act), directly or
            indirectly, of Voting Securities representing 35% or more of the
            total voting power of all the then outstanding Voting Securities; or

               b. any Initial Investor is or becomes the "beneficial owner" (as
            defined in Rule 13d-3 under the Exchange Act), directly or
            indirectly, of Voting Securities representing 50% or more of the
            total voting power of all the then outstanding Voting Securities; or

               c. the individuals who, as of the date hereof, constitute the
            Board of Directors of the Company (the "Board") together with those
            who become directors subsequent to such date and whose
            recommendation, election or nomination for election to the Board was
            approved by a vote of at least a majority of the directors then
            still in office who either were directors as of such date or whose
            recommendation, election or nomination for election was previously
            so approved, cease for any reason to constitute a majority of the
            members of the Board; or

               d. the consummation of a merger, consolidation, recapitalization,
            liquidation, sale or disposition by the Company of all or
            substantially all of the Company's assets, or reorganization of the
            Company, other than any such transaction which would (x) result in
            at least 60% of the total voting power represented by the voting
            securities of the surviving entity or, in the case of an asset sale,
            the successor entity, outstanding immediately after such transaction
            being beneficially owned, directly or indirectly, by the
            stockholders of the Company immediately preceding the transaction
            and (y) not otherwise be deemed a Change in Control under
            subparagraphs a, b, c or e of this paragraph (f); or

               e. the Board adopts a resolution to the effect that, for purposes
            hereof, a Change in Control has occurred;

            PROVIDED, HOWEVER, that a Change in Control for purposes hereof
            shall not be deemed to have occurred in connection with the
            transactions described in the Asset Purchase Agreement, dated as of
            January 10, 2000, among the Company, Risk Capital Reinsurance

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            Company, Folksamerica Holding Company, Inc. and Folksamerica
            Reinsurance Company.

        2.  All other provisions of the Options shall remain in full force and
effect. This amendment shall be governed by and construed in accordance with the
laws of the State of New York, without giving effect to principles of conflict
of laws, and may be executed in two counterparts, each of which shall constitute
one and the same instrument.

                                       2
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        IN WITNESS WHEREOF, the undersigned have executed this agreement as of
March 22, 2000.

                                          ARCH CAPITAL GROUP LTD.

                                          By:   /s/ Peter A. Appel
                                             -----------------------------------
                                             Peter A. Appel
                                             President and Chief Executive
                                             Officer

                                                /s/ Robert Clements
                                             -----------------------------------
                                             Robert Clements

                                       3

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                                                                      SCHEDULE I

                                     OPTIONS

<TABLE>
<CAPTION>
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DATE OF GRANT               NUMBER OF OPTION SHARES    TYPE OF OPTION
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<S>                         <C>                        <C>
November 19, 1996           74,000                     Non-Qualified
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November 18, 1997           54,100                     Non-Qualified
--------------------------------------------------------------------------------
November 17, 1998           49,725                     Non-Qualified
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January 1, 2000             1,500                      Non-Qualified
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</TABLE><PAGE>

                                                                 Exhibit 10.1

  Confidential Materials omitted and filed separately with the Securities and
                Exchange Commission. Asterisks denote omissions.

                  SENSOR USAGE AGREEMENT REMARKETING AGREEMENT

         This Sensor Usage Agreement Remarketing Agreement ("Agreement") is made
effective as of the 8th day of September 2000, by and between AMERICORP
FINANCIAL, INC., 877 South Adams Road, Birmingham, Michigan 48009 ("AFI"), and
CAMBRIDGE HEART, INC., 1 Oak Drive, Bedford, Massachusetts 01730 ("Cambridge").

                                    RECITALS

         A. Cambridge manufactures and markets equipment known as hearTwave (the
"Equipment") used by customers (the "Customer(s)") for T-wave Alternans testing.

         B. Certain Customers of Cambridge may desire to obtain use of the
Equipment by committing to purchase an agreed amount of sensor sets (the "Sensor
Sets") each month per the terms of the sensor usage agreement (the "Sensor Usage
Agreement"). The Customers may be given an option to cancel the Sensor Usage
Agreement at the end of each twelve months of the term.

         C. AFI will pay Cambridge a mutually agreed amount for each piece of
Equipment placed in a Customer's business using the Sensor Usage Agreement. Such
amount for the Equipment shall be paid at the inception of the agreement.
Cambridge shall guarantee to ship each month a fixed amount of Sensor Sets as
specified in the Sensor Usage Agreement.

         D. AFI is willing to provide non-recourse financing for the purchase of
Equipment used with the Sensor Usage Agreement based on Cambridge's commitments
and warranties, as described in this Agreement.

                                    AGREEMENT

         NOW THEREFORE, in consideration of the mutual covenants and promises
contained herein, the parties agree to be legally bound as follows:

         1.       DEFINED TERMS.

         1.1 "Economic Return" means the economic return still owed AFI at the
time a Customer elects to cancel Sensor Usage Agreement and is calculated as the
Split of Minimum Monthly Payments due AFI (outlined in section 2 below) that are
due or would have been due through the remaining term of the Sensor Usage
Agreement discounted to its present value using a 6% discount rate and an
estimated residual value at 20% of the original Equipment cost discounted to its
present value at a 6% discount rate, plus any costs paid by AFI to repossess,
transport, store, protect, maintain and/or insure the Equipment.

         1.2 "Sensor Usage Agreement" means the program marketed by Cambridge to
prospective customers, under which a Customer would obtain use of the Equipment
purchased by AFI with the Customer committing to purchase an agreed amount of
Sensor Sets each month per the terms of the Sensor Usage Agreement.

         1.3 "Minimum Monthly Payments" means the monthly payments made by a
Customer, in an amount acceptable to AFI and Cambridge pursuant to Section 2
below.

         1.4 "Split of Minimum Monthly Payments" means the percentage of the
Minimum Monthly Payments which is distributed to AFI and Cambridge.

         1.5 "Customer" means a customer proposed by Cambridge and accepted by
AFI, pursuant to Section 2 below, for participation in the Sensor Usage
Agreement.

<PAGE>

  Confidential Materials omitted and filed separately with the Securities and
                Exchange Commission. Asterisks denote omissions.

2. ACCEPTANCE OF CUSTOMERS AND USAGE AGREEMENTS. Cambridge will notify AFI, on a
right of first refusal basis, of prospective Customers who are interested in the
Sensor Usage Agreement. Cambridge or the prospective Customer will provide
information to AFI to substantiate that the prospective Customer has an
acceptable credit standing. If AFI, at its discretion, accepts a Customer, AFI
will enter into the Sensor Usage Agreement with the Customer, purchase the
related Equipment from Cambridge and commence the Sensor Usage Agreement with
the Customer. Unless otherwise agreed in writing by both parties and/or modified
by section 7 or 8 of this Agreement, AFI shall retain [**]% of each Minimum
Monthly Payment during the thirty six month term of the Sensor Usage Agreement
(the "Split of Minimum Monthly Payments"). The balance of the Minimum Monthly
Payments shall be forwarded to Cambridge as collected each month

         3. MINIMUM PAYMENTS. Under each Sensor Usage Agreement, Cambridge will
deliver to the Customer each month the committed amount of Sensor Sets as
specified in each agreement. Sensor Sets that are requested by the Customer in
excess of the committed amount shall be separately billed and collected by
Cambridge and may not be used to offset future monthly committments.

         4. USAGE AGREEMENTS; RIGHTS UPON EXPIRATION; CONVERSION TO A LEASE.
Each Sensor Usage Agreement will have a three-year term unless otherwise agreed
to by both parties. Upon expiration of the three-year term of a Sensor Usage
Agreement and provided the Customer has paid all amounts due, the Customer will
have the option to: (i) purchase the Equipment from AFI at the then current fair
market value not to exceed [**]% of the original purchase price; (ii) return the
Equipment to AFI; or (iii) extend the Sensor Usage Agreement (in that case,
future Minimum Monthly Payments would be shared by AFI retaining [**]% and
Cambridge receiving [**]%).

         5. REPOSSESSION AND REMARKETING OF EQUIPMENT. If a Customer requests to
return the Equipment per the terms of the return option amendment in the Sensor
Usage Agreement, AFI will notify Cambridge in writing (the "Remarketing
Notice"). Upon receipt of Remarketing Notice, Cambridge will promptly: (i) make
arrangements with the Customer to pickup the Equipment; (ii) transport the
Equipment to and store the Equipment at a facility selected by Cambridge; (iii)
perform any indicated repairs to the Equipment under warranty and or repair,
maintain, and refurbish the Equipment (to a "like-new condition") at a cost not
to exceed $[**] (to be paid out Remarketing funds after AFI's Economic Return);
and (iv) remarket the Equipment for placement with another Customer. At no time
will Cambridge be required to take title to the Equipment during the Remarketing
except that Cambridge may, at its sole discretion, elect to purchase the
Equipment for Cambridge's internal use. Cambridge shall have ninety days from
the date of the Remarketing Notice to remarket the Equipment for a value greater
or equal to AFI's Economic Return (through, sale, lease, and/or Sensor Usage
Agreement) to another Customer on a non-discriminatory, non-priority, best
efforts basis ("Remarketing"). Cambridge will provide notice to AFI of any
proposed Remarketing, the terms of which must be agreed to in advance by AFI.
AFI may in its sole discretion object to any proposed Remarketing for lack of
acceptable credit standing and or achieving Economic Return only. Such approval
will not be unreasonably withheld by AFI. In the event that AFI does not accept
the proposed Remarketing, Cambridge will have the greater of the remaining
portion of the 90 days or an additional 10 days to either propose an new
customer for Remarketing or, at its sole discretion, purchase the unit for its
own internal use. Cambridge shall be entitled to keep as its fee for Remarketing
any amounts collected in excess of AFI's necessary Economic Return.

         6. RISK OF LOSS OR DAMAGE; INSURANCE. From the time of pickup until the
Equipment is remarketed to another customer: (i) Cambridge will bear the risk of
loss or damage to the Equipment: and Cambridge will maintain property and
casualty insurance in an amount sufficient to cover the replacement cost of the
Equipment.. Upon request, Cambridge will provide AFI evidence of such insurance.

         7. REMARKETING BONUS. The parties agree that beginning with the
thirteenth month of the initial Sensor Usage Agreement and every month
thereafter, the parties will calculate the following ratio: (a) the total number
of units of Equipment that have been renewed for an additional 12 months, plus
the total number of units of Equipment that have been Remarketed (since
inception of program), (b) divided by the total number of units of Equipment
that have been renewed for an additional 12 months, plus the total number of
units of Equipment that have been Remarketed, plus the total number of units of
Equipment Cambridge has failed to

                                      -2-

<PAGE>

  Confidential Materials omitted and filed separately with the Securities and
                Exchange Commission. Asterisks denote omissions.

Remarket (the "Remarketing Success Ratio"). As long as the Remarketing Success
Ratio remains at [**]% or above, AFI agrees to adjust the Split of Minimum
Monthly Payments on all active Sensor Usage Agreements currently beyond the
first twelve months as follows; (a) for months 13 to 24 to [**]% to AFI and, (b)
for months 25 to 36 to [**]% to AFI. In the event the Remarketing Success Ratio
falls below [**]% no change will be made to the original Split of Minimum
Monthly Payments outlined in section 2 above. The parties agree that any changes
to the Split of Minimum Monthly Payments for any Sensor Usage Agreement will not
be made retroactively.

         8. GUARANTEE TO DELIVER SENSOR SETS. Cambridge warrants to AFI that
Sensor Sets shall be free from defects and shipped as specified in each Sensor
Usage Agreement. In the event Cambridge fails to deliver Sensor Sets or if such
Sensor Sets are defective and the Customer refuses to pay for the Minimum
Monthly Payment, and Cambridge is unable to remedy the situation within 30 days
of the Customers' default, then AFI in its sole discretion may deduct from the
Split of Minimum Monthly Payment(s) from other accounts an amount equal to AFI's
Split of Minimum Monthly Payments for the account in question. Such adjustment
shall continue until the Customer resumes Minimum Monthly Payments. Upon the
Customer's resuming payment, AFI shall re-adjust those contracts back to the
originally agreed Split of Minimum Monthly Payments. Cambridge shall recapture
the amount of the adjustment taken by AFI from other accounts at the end of the
term from the account that refused payment. In addition to the above provisions,
should either (a) Cambridge cease to do business or (b) such failure by
Cambridge to deliver Sensor sets cause AFI material financial hardship that
cannot be cured through the increase in sensor split, then AFI, in its sole
discretion, may purchase or have produced Sensor sets on a direct basis from any
supplier or distributor of Sensor sets. Cambridge shall in this circumstance
grant AFI the irrevocable license to produce Sensor sets solely to satisfy the
Minimum Monthly Payments for existing customers of AFI only for a period
representing the earlier of, the remaining life of the Sensor Usage Agreement,
or when Cambridge is able to remedy the circumstances responsible for the
financial hardship to AFI. Cambridge agrees to provide AFI with all proprietary
information necessary to produce such Sensor sets. AFI shall be entitled during
this period to keep all Minimum Monthly Payments associated from such Sensor's.
AFI will not disclose any such proprietary information to any third party
without the prior written consent of Cambridge.

         9. COMPLIANCE WITH APPLICABLE LAWS. Cambridge will comply with
applicable laws, rules and regulations in providing the Equipment and performing
its obligations under this Agreement. Cambridge will notify AFI of applicable
laws, rules or regulations which may affect a Customer's use of the Equipment
through participation in the Sensor Usage Agreement.

         10. INDEMNIFICATION. Cambridge agrees to indemnify and hold AFI
harmless from damages resulting from the breach of this Agreement by Cambridge,
its agents, distributors or dealers or from the failure to deliver Sensor Sets,
deliver Sensor Sets free from defects, repossession, repair, maintenance,
refurbishment, or Remarketing the Equipment. AFI agrees to indemnify and hold
Cambridge harmless from damages resulting from the breach of this Agreement by
AFI. In the event of breach, misrepresentation or dispute, the prevailing party
in any legal action shall be entitled to be compensated for reasonable
attorneys' fees and legal costs.

         11. TERM. This Agreement will continue for three (3) full years and
thereafter will continue on a year-to-year basis unless canceled by either
party. In the event of termination of this Agreement, all rights and obligations
under this Agreement, as to Equipment purchased by AFI under the Sensor Usage
Agreement, shall survive such termination and shall continue in effect.

         12. GENERAL. This Agreement (which includes the above Recitals)
constitutes the final and complete agreement of the parties and supersedes all
prior agreements with regard to the subject matter hereof. This Agreement shall
not be modified unless in writing and signed by both parties. This Agreement
shall be binding upon and inure to the benefit of the parties hereto, their
respective successors, assigns and agents. This Agreement may not be assigned
(except for purposes of funding for AFI with its bank) without prior written
consent of both parties. This Agreement shall be construed and governed in
accordance with the laws of the State of Michigan. In no case shall preprinted
terms and conditions on Cambridge's standard transactional forms (e.g.,
invoices, orders, acceptances) apply between AFI and Cambridge unless expressly
agreed to outside of the preprinted form by both parties in a signed writing.

                                      -3-

<PAGE>

         IN WITNESS WHEREOF, the parties hereto have duly executed this
Agreement to be effective as of the date and year first above written.

CAMBRIDGE HEART, INC.                      AMERICORP FINANCIAL, INC.

By: /s/ Jeffrey M. Arnold                  By: /s/ Thomas Dunnigan
    --------------------------------           -----------------------------
Print Name: Jeffrey M. Arnold              Print Name: Thomas Dunnigan
            ------------------------                   ---------------------
Title: CEO                                 Title: President
       -----------------------------              --------------------------

                                      -5-

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