Document:

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                                                                    EXHIBIT 10.1

                              EMPLOYMENT AGREEMENT

     This Agreement is effective as of the 21st day of September, 2000, by and
between John E. Ahern (the "Executive") and NMT Medical, Inc., a Delaware
corporation (the "Company").

     WHEREAS, the Company wishes to employ the Executive as the President and
Chief Executive Officer and Chairman of the Board of Directors of the Company
under the terms and conditions set forth below; and

     WHEREAS, the Executive wishes to accept such employment under those terms
and conditions;

     NOW, THEREFORE, in consideration of the provisions and mutual covenants
contained in this Agreement and for other good and valuable consideration, the
Company and the Executive (the "Parties") agree as follows:

     1.  TERM OF EMPLOYMENT.
         ------------------

     The Company agrees to employ the Executive, and the Executive agrees to
serve, on the terms and conditions of this Agreement, for a period commencing as
of the date hereof (the "Effective Date") and ending on December 31, 2002, or
such shorter period as may be provided for herein.  The employment term
described above is hereinafter referred to as the "Employment Term".  The
Employment Term may be extended only in writing signed by both the Company and
the Executive.

     2.  POSITION, DUTIES, RESPONSIBILITIES.
         ----------------------------------

     During the Employment Term, the Executive shall serve as President and
Chief Executive Officer of the Company.  In such capacity, the Executive shall
report to the Board of Directors of the Company (the "Board of Directors") and
shall perform such duties and have such responsibilities of an executive nature
as are set forth in the Company's Amended and Restated By-Laws, as amended from
time to time (the "By-Laws"), and as are customarily performed by a person
holding such office, it being recognized that the Executive's duties and
responsibilities, consistent with his titles hereunder, may be changed by the
Board of Directors from time to time.  The Executive shall devote his full
business time and attention to the performance of his duties under this
Agreement.  In addition, the Executive shall serve without additional
compensation as Chairman of the Board and as a director of the Company and on
any committees of the Board of Directors, if requested, subject to the terms of
the By-Laws and, in the case of his service as a director, to the approval of
the stockholders of the Company to the extent required by applicable law and the
By-Laws.
<PAGE>

     3.  BASE SALARY.
         -----------

     During the Employment Term, the Executive shall be paid an annual base
salary of $300,000 ("Salary"), subject to deductions for social security, state
payroll and unemployment and all other legally required or authorized deductions
and withholding.  The Executive's Salary shall be payable in accordance with the
Company's standard payroll practice.  The Board of Directors shall review the
Executive's Salary at least on an annual basis, upon the anniversary of this
Agreement; provided, however, that any actual additional Salary increases shall
be in the sole discretion of the Board of Directors.

     4.  STOCK OPTIONS.
         -------------

     On the Effective Date, the Executive shall be granted a stock option (the
"Options") to purchase 150,000 shares of common stock, par value $.001 per
share, of the Company (the "Common Stock"), under the Company's 1998 Stock
Incentive Plan (the "1998 Plan").  The exercise price for the Options shall be
the closing price ($2.156) of the Common Stock on the date of grant, which date
shall be the Effective Date.  The Options shall, to the maximum extent
permissible under Section 422 of the Internal Revenue Code of 1986, as amended
(the "Code"), constitute incentive stock options, with any balance of the
Options to be treated as non-statutory stock options.  The Options shall vest in
48 equal monthly installments on each monthly anniversary of the date of grant.
Once exercisable, the Options shall remain exercisable for a period of ten (10)
years from the date of grant (the "Final Exercise Date").  Notwithstanding the
foregoing, the Options shall become immediately exercisable in the event of a
Change of Control of the Company.  For purposes of this Agreement, a "Change of
Control of the Company" shall be deemed to have occurred only upon (a) any
merger or consolidation of the Company with or into another entity as a result
of which the Common Stock is converted into or exchanged for the right to
receive cash, securities or other property or (b) any exchange of all or
substantially all shares of the Company for cash, securities or other property
pursuant to a statutory share exchange transaction.

     5.  INCENTIVE PAYMENTS.
         ------------------

     (a) 2000 Bonus.  After the completion of the Company's fiscal quarter
ending December 31, 2000 (the "Fourth Quarter") and as soon as the Company's
financial information required to be included in its Annual Report on Form 10-K
for the fiscal year 2000 is available, but in no event later than 90 days after
the end of the Fourth Quarter, the Executive shall be entitled to receive a
bonus (the "2000 Bonus") consisting of (1) a cash bonus of up to $25,000 and (2)
a stock option grant to purchase 12,500 shares of Common Stock (the "2000 Bonus
Option") provided that (i) the Executive satisfies agreed-upon financial and
other performance goals each as contained in an incentive plan for the Executive
relating to the Fourth Quarter (the "2000 Incentive Plan"), as established in
good faith by the Board of Directors in consultation with the Executive as soon
as practicable after the Effective Date, and (ii) the Company achieves an
agreed-upon profit target relating to the Fourth Quarter as contained in the
2000 Incentive Plan and as established in good faith by the Board of Directors
in consultation with the Executive as soon as practicable after the Effective
Date; provided, however, that the Board of Directors, in its reasonable
discretion, shall determine whether the Executive has satisfied such goals.  In
the event that the Executive is entitled to the 2000 Bonus, then the Executive
shall receive the 2000 Bonus prior to the Company filing its Annual Report on
Form 10-K for the fiscal year 2000.
<PAGE>

          (i) 2000 Bonus Option. The exercise price for the 2000 Bonus Option
shall be the closing price of the Common Stock on the date of grant of the 2000
Bonus Option. The 2000 Bonus Option shall, to the maximum extent permissible
under Section 422 of the Code constitute incentive stock options, with any
balance of the 2000 Bonus Option to be treated as non-statutory stock options.
The 2000 Bonus Option shall vest in 48 equal monthly installments on each
monthly anniversary of the date of grant. Once exercisable, the 2000 Bonus
Option shall remain exercisable for a period of ten (10) years from the date of
grant. Notwithstanding the foregoing, the 2000 Bonus Option shall become
immediately exercisable in the event of a Change of Control of the Company.

     (b) Annual Bonus.  Commencing with the Company's fiscal year 2001, after
the completion of the Company's fiscal year and as soon as the Company's
financial information required to be included in its Annual Report on Form 10-K
for such fiscal year is available, but in no event later than 90 days after the
end of such fiscal year, the Executive shall be entitled to receive an annual
bonus (the "Annual Bonus") consisting of (1) a cash bonus of up to $100,000 and
(2) a stock option grant to purchase 50,000 shares of Common Stock (the "Annual
Bonus Option") provided that (i) the Executive satisfies agreed-upon financial
and other performance goals each as contained in an annual incentive plan for
the Executive as established in good faith by the Board of Directors in
consultation with the Executive on an annual basis (the "Incentive Plan") and
(ii) the Company achieves an agreed-upon profit target as contained in the
Incentive Plan as established in good faith by the Board of Directors in
consultation with the Executive on an annual basis; provided, however, that the
Board of Directors, in its reasonable discretion, shall determine whether the
Executive has satisfied such goals.  In the event that the Executive is entitled
to the Annual Bonus, then the Executive shall receive the Annual Bonus prior to
the Company filing its Annual Report on Form 10-K for such fiscal year.

          (i) Annual Bonus Option. The exercise price for the Annual Bonus
Option shall be the closing price of the Common Stock on the date of grant of
Annual Bonus Option. The Annual Bonus Option shall, to the maximum extent
permissible under Section 422 of the Code constitute incentive stock options,
with any balance of the Annual Bonus Option to be treated as non-statutory stock
options. The Annual Bonus Option shall vest in 48 equal monthly installments on
each monthly anniversary of the date of grant. Once exercisable, the Annual
Bonus Option shall remain exercisable for a period of ten (10) years from the
date of grant. Notwithstanding the foregoing, the Annual Bonus Option shall
become immediately exercisable in the event of a Change of Control of the
Company.

     6.  EMPLOYEE BENEFITS.
         -----------------

     (a) Benefit Programs. During the Employment Term, the Company shall provide
the Executive and eligible family members with medical, dental, and disability
insurance and such other benefits and perquisites as are provided in the
Company's applicable plans and programs to its employees generally; provided,
that the Executive meets the qualifications therefor ("Benefits").

          (i) Notwithstanding the provisions of Section 6(a), the Company shall
pay to the Executive an amount equal to $450.81 per month, net of all taxes and
required deductions, as reimbursement for the payments made by the Executive for
his health insurance policy with Cigna Healthcare (the "Outside Health
Insurance"); provided, however, that (x) during the term of the Executive's
Outside Health Insurance, the Executive shall not be entitled to any of the
Benefits to the extent covered by the Executive's Outside Health Insurance, (y)
the Executive shall not renew his Outside Health Insurance upon its expiration
and (z) the Executive shall be entitled to the Benefits upon the expiration of
the Outside Health Insurance.
<PAGE>

     (b) Vacation. During each twelve month period of the Employment Term, the
Executive shall be entitled to no less than four weeks of vacation; provided,
however, that any vacation time not taken during any year shall be forfeited.
The Executive shall also be entitled to all paid holidays given by the Company
to its officers and employees.

     (c) Relocation Expenditures. The Company shall reimburse the Executive for
the reasonable and documented expenses incurred by the Executive for a period of
90 days following the Effective Date relating to the Executive's relocation and
temporary living expenses, including housing, meals and travel, which expenses
shall not exceed $15,000. Notwithstanding the foregoing, the Company shall not
be obligated to reimburse the Executive for any such expenses that are not
documented.

     7.  REPRESENTATIONS AND WARRANTIES OF THE EXECUTIVE.
         -----------------------------------------------

     The Executive represents and warrants to the Company that the Executive is
under no contractual or other restriction or obligation which is inconsistent
with the execution of this Agreement, the performance of his duties hereunder,
or the other rights of the Company hereunder.

     8.  NON-COMPETITION; NON-SOLICITATION.
         ---------------------------------

     In view of the unique and valuable services it is expected Executive will
render to the Company, Executive's knowledge of the customers, trade secrets,
and other proprietary information relating to the business of the Company and
its customers and suppliers and similar knowledge regarding the Company it is
expected Executive will obtain, and in consideration of the compensation to be
received hereunder, Executive agrees that he will not, during the period he is
employed by the Company under this Agreement or otherwise, and for a period of
one year after he ceases to be employed by the Company under this Agreement or
otherwise, compete with or be engaged in, or Participate In (as defined below)
any other business or organization (which shall not include a university,
hospital, or other non-profit organization) which during such one year period is
or as a result of the Executive's engagement or participation would become
competitive with the Company's business of designing, developing, manufacturing,
marketing and selling neurosurgical devices, vena cava filters, stents, septal
repair devices or other medical devices being designed, developed, manufactured,
marketed or sold by the Company up to the time of such cessation; provided,
however, that the provisions of this Section 8 shall not be deemed breached
merely because the Executive owns less than 1% of the outstanding capital stock
of a corporation, if, at the time of its acquisition by the Executive such stock
is listed on a national securities exchange.  The term "Participate In" shall
mean:  "directly or indirectly, for his own benefit or for, with or through any
other person (including the Executive's immediate family), firm or corporation,
own, manage, operate, control, loan money to, or participate in the ownership,
management, operation or control of, or be connected as a director, officer,
employee, partner, consultant, agent, independent contractor, or otherwise with,
or acquiesce in the use of his name in."
<PAGE>

     The Executive will not, directly or indirectly, solicit or interfere with,
or endeavor to entice away from the Company any of its suppliers, customers or
employees within a period of one year after the date of termination of the
Executive's employment (the "Termination Date").  The Executive will not
directly or indirectly employ any person who was an employee of the Company
within a period of one year after such person leaves the employ of the Company.

     If any restriction contained in this Section 8 shall be deemed to be
invalid, illegal, or unenforceable by reason of the extent, duration or
geographical scope thereof, or otherwise, then the court making such
determination shall have the right to reduce such extent, duration, geographical
scope or other provisions hereof, and in its reduced form such restriction shall
then be enforceable in the manner contemplated hereby.

     9.  INTELLECTUAL PROPERTY RIGHTS.
         ----------------------------

     Any interest in patents, patent applications, inventions, technological
innovations, copyrights, copyrightable works, developments, discoveries, designs
and processes which the Executive during the period he is employed by the
Company under this Agreement or otherwise may acquire, conceive of or develop,
either alone or in conjunction with others, utilizing the time, material,
facilities or information of the Company ("Inventions") shall belong to the
Company; as soon as the Executive owns, conceives of, or develops any Invention,
he agrees immediately to communicate such fact in writing to the Board of
Directors, and without further compensation, but at the Company's expense,
forthwith upon request of the Company, the Executive shall execute all such
assignments and other documents (including applications for patents, copyrights,
trademarks, and assignments thereof) and take all such other action as the
Company may reasonably request in order (a) to vest in the Company all of the
Executive's right, title and interest in and to such Inventions, free and clear
of liens, mortgages, security interests, pledges, charges and encumbrances and
(b), if patentable or copyrightable, to obtain patents or copyrights (including
extensions and renewals) therefor in any and all countries in such name as the
Company shall determine.

     10.  NONDISCLOSURE.
          -------------

     The Employee Nondisclosure and Secrecy Agreement dated as of September 21,
2000 between the Company and the Executive shall remain in full force and
effect.

     11.  INJUNCTIVE RELIEF.
          -----------------

     Because a breach of the provisions of any of Section 8, Section 9 and
Section 10 could not adequately be compensated by money damages, the Company
shall be entitled, in addition to any other right and remedy available to it, to
an injunction restraining such breach or a threatened breach, and in either case
no bond or other security shall be required in connection therewith.  The
Executive agrees that the provisions of each of Section 8, Section 9 and Section
10 are necessary and reasonable to protect the Company in the conduct of its
business.
<PAGE>

     12.  TERMINATION OF THE EXECUTIVE UPON DEATH OR DISABILITY.
          -----------------------------------------------------

     (a) The term of the Executive's employment shall terminate automatically
upon his death. In addition, the Company shall have the right to terminate the
Employment Term upon the Disability (as defined below) of the Executive. If the
Executive's employment is terminated by the Company due to the Executive's death
or Disability, then the Executive, his guardian or his estate, as applicable,
shall be entitled to:

          (i)  Salary and Benefits earned to the Termination Date; and

          (ii) other benefits as are provided under the applicable plans and
               programs of the Company as then in effect.

     (b) In addition, if the Executive's employment is terminated due to his
death or Disability, and the Company has not terminated the Executive's
employment for Cause pursuant to Section 14 below, any of the Options, 2000
Bonus Option and the Annual Bonus Options shall remain exercisable to the extent
that any of the Options, 2000 Bonus Option and the Bonus Options were
exercisable on the date of the Executive's death or Disability for a period of
one year following the Termination Date pursuant to this Section 12(b), and
shall thereafter expire.

     (c) For purposes of this Agreement, "Disability" shall mean any physical or
mental disability or incapacity that renders the Executive incapable of
performing his duties hereunder for a period of 180 consecutive calendar days or
for shorter periods aggregating 180 calendar days during any consecutive twelve-
month period.

     13.  INVOLUNTARY TERMINATION WITHOUT CAUSE.
          -------------------------------------

     (a)  The Executive shall be deemed to have been involuntarily terminated
 without Cause (as defined below) if one of the following events occurs:

          (i)   The Company terminates the Executive's employment at anytime
                without Cause (as defined below);

          (ii)  There occurs a substantial reduction by the Company in the
                Executive's responsibilities, authorities, powers and duties
                from the responsibilities, authorities, powers and duties
                exercised by the Executive just prior to such reduction but
                excluding such reduction effected with the Executive's prior
                consent or for reasons arising out of the Executive's gross
                negligence or willful misconduct;

          (iii) The Company requires the Executive to be based principally at
                any office or location which is outside New England, unless the
                Executive consents to be based principally at another office or
                location;

          (iv)  Subject to Section 6(a)(i) of this Agreement, the Company's
                failure to (x) maintain the Executive's eligibility for
                participation in existing benefit plans then being made
                available by the Company to other employees of the Company
                having substantially similar levels of responsibility as the
                Executive or (y) provide to the Executive substantially the
                same benefits or other perquisites then being provided or
                paid to the other employees of the Company having
                substantially similar levels of responsibility as the
                Executive; or
<PAGE>

          (v)   There occurs a breach of this Agreement by the Company which
                continues for more than seven (7) business days after the
                Executive gives written notice to the Company, setting forth
                in reasonable detail the nature of such breach.

     (b)  If the Executive's employment is involuntarily terminated at any time
without Cause (as defined below), the Executive shall be entitled to:

          (i)   Salary and Benefits earned to the Termination Date;

          (ii)  Any of the 2000 Bonus and Annual Bonus as accrued to the
                Termination Date; provided, however, that the Board of
                Directors, in its reasonable discretion, shall determine
                whether the Executive has satisfied the conditions to the
                Executive's receipt of each of the 2000 Bonus and Annual
                Bonus; and

          (iii) Continued Salary for a period of six months from the
                Termination Date.

     In addition, all exercisable Options, 2000 Bonus Option and Annual Bonus
Options shall expire 90 days after the Termination Date.

     14.  TERMINATION BY THE COMPANY FOR CAUSE.
          ------------------------------------

     (a)  GENERAL. The Company shall have the right to terminate the Executive's
employment for Cause, as defined in subsection (b) below, in which event, the
Executive shall be entitled only to Salary and Benefits earned to the
Termination Date. In addition, all exercisable Options, 2000 Bonus Option and
Annual Bonus Options shall expire as of the Termination Date.

     (b)  CAUSE.  For purposes of this Agreement, "Cause" shall mean:

          (i)   fraud, embezzlement or gross insubordination on the part of
                the Executive;

          (ii)  conviction of or the entry of a plea of nolo contendere by
                the Executive to any felony or crime of moral turpitude;

          (iii) a material breach of, or the willful failure or refusal by
                the Executive to perform and discharge, his duties,
                responsibilities or obligations under this Agreement that is
                not corrected within 20 days following written notice
                thereof to the Executive by the Company, such notice to
                state with specificity the nature of the breach, failure or
                refusal; provided, that if such breach, failure or refusal
                cannot reasonably be corrected within 20 days of written
                notice thereof, correction shall be commenced by the
                Executive within such period and shall be corrected as soon
                as practicable thereafter; or
<PAGE>

          (iv)  any act of willful misconduct by the Executive which is
                intended to result in substantial personal enrichment of the
                Executive at the expense of the Company or any of its
                subsidiaries or affiliates.

     15.  TERMINATION BY THE EXECUTIVE WITHOUT CAUSE.  The Executive may
          ------------------------------------------
terminate this Agreement at any time with or without cause by providing thirty
(30) days' prior written notice to the Company, in which event, the Executive
shall be entitled only to Salary and Benefits earned to the Termination Date.
In addition, all exercisable Options, 2000 Bonus Option and Annual Bonus Options
shall expire 90 days after the Termination Date.

     16.  WITHHOLDING.
          -----------

     Anything to the contrary notwithstanding, all payments required to be made
by the Company under this Agreement to the Executive, his spouse, his estate or
beneficiaries, shall be subject to withholding of such amounts relating to taxes
as the Company may reasonably determine it should withhold pursuant to any
applicable law or regulation.  In addition, in the event that the Company
reasonably determines that it is required to make any payments of withholding
taxes as a result of Executive's receipt of any other income pursuant to the
terms of this Agreement, the Company may, as a condition to such receipt,
require that the Executive provide the Company with an amount of cash sufficient
to enable the Company to pay such withholding taxes.

     17.  LOCK-UP AGREEMENT.
          ------------------

     In the event that the Company seeks to consummate a public offering of its
securities during the Employment Term, the Executive shall execute an agreement
in a form and substance satisfactory to the managing underwriter or underwriters
of the Company's securities, not to sell, pledge, contract to sell, grant any
option or otherwise dispose of any shares of stock owned or acquired by the
Executive for such period of time as requested by such underwriter of all other
executive officers of the Company.

     18.  INDEMNIFICATION.
          ---------------

     During the Employment Term, the Company agrees (i) to indemnify the
Executive in his capacity as an officer and director of the Company and, to the
extent applicable, each subsidiary of the Company, as provided in Article Eighth
of the Company's Second Amended and Restated Certificate of Incorporation, as
amended, and (ii) use its best efforts to maintain in effect its director and
officer liability insurance policies.
<PAGE>

     19.  LEGAL FEES.
          ----------

     The Company shall reimburse the Executive all reasonable and documented
legal fees, costs and expenses incurred by the Executive in contesting or
disputing any breach of this Agreement by the Company or in seeking to obtain or
enforce any right or benefit provided by this Agreement; provided, however, that
the Company shall have no such obligation to reimburse the Executive for such
legal fees, costs and expenses unless the final resolution of such matter is
determined by a court of competent jurisdiction to be in the Executive's favor.

     20.  ASSIGNABILITY; BINDING NATURE.
          -----------------------------

     This Agreement and all rights of the Executive shall inure to the benefit
of and be enforceable by the Executive's personal or legal representatives,
estates, executors, administrators, heirs and beneficiaries.  All amounts
payable to the Executive hereunder shall be paid, in the event of the
Executive's death, to the Executive's estate, heirs and representatives.  This
Agreement shall inure to the benefit of, be binding upon, and be enforceable by,
any successor, surviving or resulting company or other entity to which all or
substantially all of the Company's business and assets shall be transferred.

     21.  ENTIRE AGREEMENT.
          ----------------

     This Agreement, together with the Employee Nondisclosure and Secrecy
Agreement, contains the entire agreement between the Executive and the Company
(each, a "Party") concerning the subject matter hereof and supersedes all prior
agreements, understandings, discussions, negotiations, and undertakings, whether
written or oral, between the Parties with respect thereto.

     22.  AMENDMENTS AND WAIVERS.
          ----------------------

     This Agreement may not be modified or amended except by a writing signed by
both Parties.  A Party may waive compliance by the other Party with any term or
provision of this Agreement, or any part thereof, provided that the term or
provision, or part thereof, is for the benefit of the waiving Party.  Any waiver
will be limited to the facts or circumstances giving rise to the noncompliance
and will not be deemed either a general waiver or modification with respect to
the term or provision, or part thereof, being waived, or as to any other term or
provision of this Agreement, nor will it be deemed a waiver of compliance with
respect to any other facts or circumstances then or thereafter occurring.

     23.  NOTICE.
          ------

     Any notice given under this Agreement shall be in writing and shall be
deemed given when delivered personally or by courier, or five days after being
mailed, certified or registered mail, duly addressed to the Party concerned at
the address indicated below or at such other address as such Party may
subsequently provide, in accordance with the notice and delivery provisions of
this Section 23:
<PAGE>

    To the Company:                NMT Medical, Inc.
                                   27 Wormwood Street
                                   Boston, MA  02210
                                   Attn.:  Board of Directors

     with a copy to:               Hale and Dorr LLP
                                   60 State Street
                                   Boston, MA  02109-1803
                                   Attn:  Steven D. Singer, Esq.

     To the Executive:             John E. Ahern
                                   1120 Edson Hill Road
                                   Stowe, VT  05672

     with a copy to:               Edwards & Angell, LLP
                                   101 Federal Street
                                   Boston, MA  02110-1800
                                   Attn:  Jonathan M. Lourie, Esq.

     24.  SEVERABILITY.
          ------------

     In the event that any provision or portion of this Agreement shall be
determined to be invalid or unenforceable for any reason, the remaining
provisions or portions of this Agreement will be unaffected thereby and shall
remain in full force and effect to the fullest extent permitted by law.

     25.  SURVIVORSHIP.
          ------------

     The respective rights and obligations of the Parties hereunder shall
survive any termination of this Agreement to the extent necessary to the
intended preservation of such rights and obligations.

     26.  REFERENCES.
          ----------

     In the event of the Executive's death or a judicial determination of his
incompetence, reference in this Agreement to the Executive shall be deemed,
where appropriate, to refer to his legal representative or, where appropriate,
to his beneficiary or beneficiaries.

     27.  GOVERNING LAW.
          -------------

     This Agreement shall be governed by and construed and interpreted in
accordance with the laws of The Commonwealth of Massachusetts without reference
to the principles of conflicts of law.

     28.  HEADINGS.
          --------

     The headings of sections contained in this Agreement are for convenience
only and shall not be deemed to control or affect the meaning or construction of
any provision of this Agreement.
<PAGE>

     29.  COUNTERPARTS.
          ------------

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

        [The remainder of this page has been intentionally left blank.]
<PAGE>

     THE UNDERSIGNED have executed this Agreement effective as of the date first
written above.

                                       COMPANY:

                                       NMT Medical, Inc.

                                       By: /s/ Randall W. Davis
                                           ------------------------
                                           Name: Randall W. Davis
                                                 ------------------
                                           Title: Acting President
                                                 ------------------

                                       EXECUTIVE:

                                        /s/ John E. Ahern
                                        ---------------------------
                                        John E. Ahern<PAGE>

                                                                    EXHIBIT 10.2

                           WAIVER AND AMENDMENT NO. 4
                           --------------------------

     This Waiver and Amendment No. 4, made as of November 13, 2000 (this
"Waiver"), is by and among NMT Medical, Inc. (the "Company"), on the one hand,
and Whitney Subordinated Debt Fund, L.P. (the "Purchaser"), on the other hand.
Capitalized terms used herein and not otherwise defined have the meanings
assigned to such terms in the Purchase Agreement (as defined below).

                              W I T N E S S E T H:

     WHEREAS, the Company and the Purchaser are parties to the Subordinated Note
and Common Stock Purchase Agreement, dated as of July 8, 1998, as amended by (i)
Amendment No. 1, dated April 14, 1999, (ii) Amendment No. 2, dated September 13,
1999, and (iii) Amendment No. 3, dated as of April 5, 2000, by and among the
Company, the Purchaser, and, for certain purposes, J. H. Whitney & Co. (as so
amended, the "Purchase Agreement"), regarding the Company's $20,000,000
subordinated notes due September 30, 2003;

     WHEREAS, the Company has requested the Purchaser to waive compliance with
certain covenants contained in the Purchase Agreement for the fiscal quarter
ended September 30, 2000 and the Company and Purchaser wish to amend the
Purchase Agreement to provide that certain information will be provided and
certain covenant compliance will be tested on a monthly basis.

     NOW, THEREFORE, in consideration of the premises and mutual agreements
contained herein, and other good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, the parties hereto agree as
follows:

1.    The Purchaser hereby waives compliance by the Company with the provisions
of Sections 9.8(a), (b), (c), (e) and (f) of the Purchase Agreement solely with
respect to the fiscal quarter ended September 30, 2000.

2.    The Company acknowledges and agrees that the Company is required to and
shall deliver to Purchaser, as soon as available and in any event within thirty
(30) days after the end of each month, beginning with November 2000, the
consolidated balance sheet of the Company and its Subsidiaries, as at the end of
such month and the related consolidated statements of operations, stockholders'
equity (deficit) and cash flow for such month and for the period from the
beginning of the then current fiscal year of the Company to the end of such
month (and, with respect to financial statements delivered for

                                       1
<PAGE>

months that are also the last month of any fiscal quarter, accompanied by the
related consolidated statements of operations, stockholders' equity (deficit)
and cash flow for such fiscal quarter) and a schedule of the outstanding
Indebtedness for borrowed money of the Company and its Subsidiaries describing
in reasonable detail each such debt issue or loan outstanding and the principal
amount and amount of accrued and unpaid interest with respect to each such debt
issue or loan. The Company and Purchaser confirm and agree that the financial
covenants continued in Sections 9.8 (a)(b)(c) and (f) which require compliance
as of the end of the calendar quarter shall be and are hereby amended to require
such compliance as of the end of each month beginning November 30, 2000 and,
accordingly, wherever there appears in Sections 9.8 (a)(b)(c) and (f) the term
"the last day of a calendar quarter" or any similar term, same shall be and
hereby is amended to refer to "the last day of a month".

3.    This Waiver may be signed in counterparts, and by the various parties on
separate counterparts. Each set of counterparts which contains the signature of
each of the parties shall constitute a single instrument with the same effect as
if the signature thereto were upon the same instrument. The parties hereto agree
that each party shall accept facsimile signatures as legally sufficient, binding
and admissible evidence of the execution of this Waiver.

4.    Except as expressly modified by this Waiver, all of the terms and
provisions of the Purchase Agreement, by and among the Company and the
Purchaser, and the Notes shall continue in full force and effect and all parties
hereto shall be entitled to the benefits thereof

5.    This Waiver shall be governed by and construed in accordance with the laws
of the State of New York, without regard to the principles of conflict of laws
of such state.

     IN WITNESS WHEREAS, the parties hereto have caused this Waiver to be signed
by their respective duly authorized officers as of the date first written above.

                            NMT MEDICAL, INC.

                            By: /s/ John E. Ahern
                               ------------------------------------------
                            Name:  John E. Ahern
                            Title:  President and Chief Executive Officer

                            WHITNEY SUBORDINATED DEBT FUND, L.P.

                            By: /s/ James H. Fordyce
                               ------------------------------------------
                            Name:  James H. Fordyce
                            Title: A General Partner

                                       2

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