-----BEGIN PRIVACY-ENHANCED MESSAGE-----
Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
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MIC-Info: RSA-MD5,RSA,
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 K2MPU5QvwwfVr/qUWixYEA==

<SEC-DOCUMENT>0001179110-05-014395.txt : 20050718
<SEC-HEADER>0001179110-05-014395.hdr.sgml : 20050718
<ACCEPTANCE-DATETIME>20050718171524
ACCESSION NUMBER:		0001179110-05-014395
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20050714
FILED AS OF DATE:		20050718
DATE AS OF CHANGE:		20050718

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			NMT MEDICAL INC
		CENTRAL INDEX KEY:			0001017259
		STANDARD INDUSTRIAL CLASSIFICATION:	SURGICAL & MEDICAL INSTRUMENTS & APPARATUS [3841]
		IRS NUMBER:				954090463
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		27 WORMWOOD STREET
		CITY:			BOSTON
		STATE:			MA
		ZIP:			02210
		BUSINESS PHONE:		6177370930

	MAIL ADDRESS:	
		STREET 1:		27 WORMWOOD STREET
		CITY:			BOSTON
		STATE:			MA
		ZIP:			02210

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	NITINOL MEDICAL TECHNOLOGIES INC
		DATE OF NAME CHANGE:	19960619

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			CASTLEMAN PETER M
		CENTRAL INDEX KEY:			0001239594

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-21001
		FILM NUMBER:		05960022

	BUSINESS ADDRESS:	
		STREET 1:		WHITNEY & CO.
		STREET 2:		177 BROAD STREET
		CITY:			STAMFORD
		STATE:			CT
		ZIP:			06901
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>edgar.xml
<DESCRIPTION>FORM 4 -
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2005-07-14</periodOfReport>

    <notSubjectToSection16>1</notSubjectToSection16>

    <issuer>
        <issuerCik>0001017259</issuerCik>
        <issuerName>NMT MEDICAL INC</issuerName>
        <issuerTradingSymbol>NMTI</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001239594</rptOwnerCik>
            <rptOwnerName>CASTLEMAN PETER M</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>177 BROAD STREET, 15TH FLOOR</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>STAMFORD</rptOwnerCity>
            <rptOwnerState>CT</rptOwnerState>
            <rptOwnerZipCode>06901</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common</value>
            </securityTitle>
            <transactionDate>
                <value>2005-07-14</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>J</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F4"/>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>1829010</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>10.8620</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See Footnote 1.</value>
                    <footnoteId id="F1"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common</value>
            </securityTitle>
            <transactionDate>
                <value>2005-07-14</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>J</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F5"/>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>561207</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>10.90</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See Footnote 2.</value>
                    <footnoteId id="F2"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>113793</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See Footnote 3.</value>
                    <footnoteId id="F3"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">Securities owned by Whitney Equity Partners, L.P. (&quot;Equity Partners&quot;).  The undersigned is a managing member of J. H. Whitney Equity Partners, L.L.C., the general partner of Equity Partners, and has an interest in two limited partners of Equity Partners.  The undersigned may be deemed to share voting and dispositive power with respect to such shares.  The undersigned disclaims beneficial ownership of such shares except to the extent of his proportionate interest.</footnote>
        <footnote id="F2">Securities owned by Whitney Subordinated Debt Fund, L.P. (&quot;Debt Fund&quot;).  The undersigned is a managing member of Whitney General Partner, L.L.C., the general partner of Debt Fund.  The undersigned may be deemed to share voting and dispositive power with respect to such shares.  The undersigned disclaims beneficial ownership of such shares except to the extent of his proportionate interest.</footnote>
        <footnote id="F3">Securities owned by J. H. Whitney &amp; Co. (&quot;JHW&amp;Co.&quot;).   The undersigned is a managing member of Whitney General Partner, L.L.C., the general partner of JHW&amp;Co.  The undersigned may be deemed to share voting and dispositive power with respect to such shares.  The undersigned disclaims beneficial ownership of such shares except to the extent of his proportionate interest.</footnote>
        <footnote id="F4">Securities distributed to partners of Equity Partners on a pro-rata basis in accordance with the Partnership Agreement.</footnote>
        <footnote id="F5">Securities distributed to partners of Debt Fund on a pro-rata basis in accordance with the Partnership Agreement.</footnote>
    </footnotes>

    <remarks>Equity Partners, Debt Fund and JHW&amp;Co. may be deemed members of a Section 13(d) &quot;group&quot;.  The undersigned disclaims the existence of such a group and disclaims beneficial ownership of the Common Stock owned by such partnerships, except as set forth in Footnotes 1, 2 and 3.</remarks>

    <ownerSignature>
        <signatureName>Peter M. Castleman, By:  Daniel J. O'Brien, Attorney-in-Fact</signatureName>
        <signatureDate>2005-07-18</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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