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CAMBRIDGE HEART
                                                                   Exhibit 10.34


                                        Nobember 18, 1999



Jim Sheppard
VP of Operations
Cambridge Heart, Inc.
One Oak Park Drive
Bedford, MA  01730



Re:  Severance Agreement

Dear Jim:

     Cambridge Heart, Inc. (the "Company") recognizes that, as is the case with
many publicly-held corporations, the possibility of a change in control of the
Company exists and that such possibility, and the uncertainty and questions it
may raise among key personnel, may result in the departure or distraction of key
personnel to the detriment of the Company and its stockholders. The Board of
Directors has determined that, while there are no current plans for the Company
to engage in a change of control transaction, appropriate steps be taken to
reinforce and encourage the continued employment and dedication of the Company's
key personnel without distraction from the possibility of a change of control
and related events and circumstances.

     Accordingly, the Company agrees as follows:

     1.  In the event that the Company terminates your employment without Cause,
then the following shall apply:

         .  You will continue to be paid your salary for six (6) months after
            termination at the rate in effect on the termination date.

         .  You will continue for six (6) months to be enrolled in the health
            insurance program you were enrolled in as of the termination date.

         .  The vesting of all stock options you hold as of the termination date
            will be accelerated as follows: the number of shares under all such
            options that would have become vested (i.e., exercisable) during the
            twelve (12) month period following the termination date shall become
            exercisable; you must exercise all options (including the
            accelerated portion) within the time periods set forth in your
            option agreement(s) and the applicable option plan.



       Cambridge Heart, Inc. * 1 Oak Park Drive * Bedford, MA  01730 *
                    Phone: 781-271-1200 * Fax: 781-275-8431
                             www.cambridgeheart.com
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     2.   In the event that a Change in Control occurs, the following shall
apply:

          .  The vesting of all stock options you hold as of the Change in
             Control Date will be accelerated as follows: fifty percent (50%) of
             the number of shares under all such options that were not vested
             (i.e., exercisable) as of the Change in Control Date shall become
             exercisable as of the Change in Control Date; you must exercise all
             options (including the accelerated portion) within the time periods
             set forth in your options agreement(s) and the applicable option
             plan.

     3.   In the event that a Change in Control occurs and, within twelve (12)
months after the Change in Control Date, your employment (either with the
Company or the successor/acquiror) is terminated without Cause or you terminate
your employment for Good Reason, then the following shall apply:

          .  You will continue to be paid your salary for twelve (12) months
             after termination at the rate in effect on the termination date.

          .  You will continue for twelve (12) months to be enrolled in the
             health insurance program you were enrolled in as of the termination
             date.

          .  The vesting of all stock options you hold as of the Change in
             Control Date will be accelerated as follows: one hundred percent
             (100%) of the number of shares under all such options that were not
             vested (i.e., exercisable) as of the termination date shall become
             exercisable as of the termination date; you must exercise all
             options (including the accelerated portion) within the time periods
             set forth in your options agreement(s) and the applicable option
             plan.

All capitalized terms used in this letter agreement have the meanings set forth
in Exhibit A.
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This agreement supersedes all other agreements concerning severance.

          Sincerely yours,

          CAMBRIDGE HEART, INC.


          By: /s/ Jeffrey Arnold
             -------------------------------------
          Title: /s/ President
                ----------------------------------

AGREED:


/s/ James W. Sheppard
-----------------------------------------
Employee



       Cambridge Heart, Inc. - 1 Oak Park Drive - Bedford, MA  01730 -
                    Phone: 781-271-1200 - Fax: 781-275-8431
                             www.cambridgeheart.com
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                                   EXHIBIT A
                                   ---------


        1.  "Change in Control" means an event or occurrence set forth in any
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one or more subsections (a) through (c) below (including an event or occurrence
that constitutes a Change in Control under one of such subsections but is
specifically exempted from another such subsection):

            (a)  the acquisition by an individual, entity or group (within the
meaning of Section 13(d)(3) or 14(d)(2) of the Securities Exchange Act of 1934,
as amended (the "Exchange Act")) (a "Person") of beneficial ownership of any
capital stock of the Company if, after such acquisition, such Person
beneficially owns (within the meaning of Rule 13d-3 promulgated under the
Exchange Act) 50% or more of either (i) the then-outstanding shares of common
stock of the Company (the "Outstanding Company Common Stock") or (ii) the
combined voting power of the then-outstanding securities of the Company entitled
to vote generally in the election of directors (the "Outstanding Company Voting
Securities"); provided, however, that for purposes of this subsection (a), the
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following acquisitions shall not constitute a Change in Control; (i) any
acquisition directly from the company, (ii) any acquisition by the Company or
(iii) any acquisition by any employee benefit plan (or related trust) sponsored
or maintained by the Company or any corporation controlled by the Company; or


            (b)  such time as the Continuing Directors (as defined below) do not
constitute a majority of the Board (or, if applicable, the Board of Directors
of a successor corporation to the Company), where the term "Continuing Director"
means at any date a member of the Board (i) who was a member of the Board on the
date of the execution of this Agreement or (ii) who was nominated or elected
subsequent to such date by at least a majority of the directors who were
Continuing Directors at the time of such nomination or election or whose
election to the Board was recommended or endorsed by at least a majority of the
directors who were Continuing Directors at the time of such nomination or
election; or


            (c)  the consummation of a merger, consolidation, reorganization,
recapitalization or statutory share exchange involving the Company or a sale or
other disposition of all or substantially all of the assets of the Company (a
"Business Combination"), unless, immediately following such Business
Combination, all or substantially all of the individuals and entities who were
the beneficial owners of the Outstanding Company Common Stock and Outstanding
Company Voting Securities immediately prior to such Business Combination
beneficially own, directly or indirectly, more than 50% of the then-outstanding
shares of common stock and combined voting power of the then-outstanding
securities entitled to vote generally in the election of directors,
respectively, of the resulting or acquiring corporation in such Business
Combination in substantially the same proportions as their ownership,
immediately prior to such Business Combination, of the Outstanding Company
Voting Securities, respectively.


        2.   "Change in Control Date" means the first date on which a Change
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in Control occurs.

                                       2

        Cambridge Heart, Inc. * 1 Oak Park Drive * Bedford, MA 01730 *
                    Phone: 781-271-1200  Fax: 781-275-8431
                            www.cambridgeheart.com
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    3. "Cause" means;
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    (a) the Employee's willful and continued failure to substantially perform
[his/her] reasonable assigned duties (other than any such failure resulting from
incapacity due to physical or mental illness or any failure after the Employee
gives notice of termination for Good Reason), which failure is not cured within
30 days after a written demand for substantial performance is received by the
Employee from the Board of Directors of the Company which specifically
identifies the manner in which the Board of Directors believes the Employee has
not substantially performed the Employee's duties; or

    (b) the Employee's willful engagement in illegal conduct or gross misconduct
which is materially and demonstrably injurious to the Company.

  For purposes of this Section 3, no act or failure to act by the Employee shall
be considered "willful" unless it is done, or omitted to be done, in bad faith
and without reasonable belief that the Employee's action or omission was in the
best interests of the Company.

    4. "Good Reason" means the occurrence, without the Employee's written
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consent, of any of the events or circumstances set forth in clauses (a) through
(d) below Notwithstanding the occurences of any such event or circumstance,
such occurrence shall not be deemed to constitute Good Reason if, prior to the
notice of termination given by the Employee in respect thereof, such event or
circumstance has been fully corrected and the Employee has been reasonably
compensated for any losses or damages resulting therefrom (provided that such
right of correction by the Company shall only apply to the first notice of
termination for Good Reason given by the Employee).

        (a) the assignment to the Employee of duties inconsistent in any
material respect with the Employee's position (including status, offices, titles
and reporting requirements), authority or responsibilities in effect immediately
prior to the earliest to occur of (i) the Change is Control Date, (ii) the date
of the execution by the Company of the initial written agreement or instrument
provided for the Change in Control or (iii) the date of the adoption by the
Board of Directors of a resolution providing for the Change in Control (with the
earliest to occur of such dates returned to herein as the "Measurement Date"),
or any other action or omission by the Company which results is a diminution in
such position, authority or responsibilities;

        (b) a reduction is the Employee's annual base salary as in effect on the
Measurment Date or as the same was or may be increased from time to time;


        (c) the failure by the Company to (i) continue in effect any material
compensation or benefit plan or program (including without limitation any life
insurance, medical, health and accident or disability plan and any vacation
program or policy) (a "Benefit Plan") in which the Employee participates or
which is applicable to the Employee immediately prior to the Measurement Date,
unless an equitable arrangement (embodied in an ongoing substitute or
alternative plan) has been made with respect to such plan or program, (ii)
continue the Employee's participation therein (or in such substitute or
alternative plan) on a basis not materially less favorable, both in terms of the
amount of benefit provided and the level of the Employee's participation
relative to other participants, than the basis existing immediately prior to the
Measurement Date or (iii) award cash bonuses to the Employee in amounts and in a
manner substantially consistent with past practice in light of the Company's
financial performance;

                                       3

         CAMBRIDGE HEART, Inc. * 1 Oak Park Drive * Bedford, MA 01730 *
                    Phone: 781-271-1200 * Fax: 781-275-8431
                             www.cambridgeheart.com
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        (D)  any failure of the Company to pay or provide to the Employee any
portion of the Employee's compensation or benefits due under any Benefit Plan
within seven days of the date such compensation or benefits are due, or any
material breach by the Company of any employment agreement with the Employee.


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