<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0202</schemaVersion>

    <documentType>4/A</documentType>

    <periodOfReport>2006-03-16</periodOfReport>

    <dateOfOriginalSubmission>2006-03-16</dateOfOriginalSubmission>

    <notSubjectToSection16>0</notSubjectToSection16>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001245310</rptOwnerCik>
            <rptOwnerName>DAVIS RICHARD E</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>NMT MEDICAL, INC.</rptOwnerStreet1>
            <rptOwnerStreet2>27 WORMWOOD STREET</rptOwnerStreet2>
            <rptOwnerCity>BOSTON</rptOwnerCity>
            <rptOwnerState>MA</rptOwnerState>
            <rptOwnerZipCode>02110</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>V.P. &amp; Chief Financial Officer</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2006-03-16</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>M</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>8854</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>1.25</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>77611</value>
                    <footnoteId id="F1"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2006-03-16</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>M</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>1875</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>1.76</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>79486</value>
                    <footnoteId id="F2"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2006-03-16</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>M</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>11500</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>5.03</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>90986</value>
                    <footnoteId id="F3"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Option (Right to Buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>5.03</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2006-03-16</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>M</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>11500</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>5.03</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2002-03-07</value>
                <footnoteId id="F5"/>
            </exerciseDate>
            <expirationDate>
                <value>2012-03-06</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>11500</value>
                    <footnoteId id="F4"/>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>11500</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">The reporting person originally reported this transaction on a Form 4 filed on March 16, 2006.  The reporting person mistakenly reported the number of shares of common stock beneficially owned following the reported transaction as 78,611 in the original Form 4.  Following the reported transaction, the reporting person owned only 77,611 shares of common stock.</footnote>
        <footnote id="F2">The reporting person originally reported this transaction on a Form 4 filed on March 16, 2006.  The reporting person mistakenly reported the number of shares of common stock beneficially owned following the reported transaction as 80,486 in the original Form 4.  Following the reported transaction, the reporting person owned only 79,486 shares of common stock.</footnote>
        <footnote id="F3">The reporting person originally reported this transaction on a Form 4 filed on March 16, 2006.  The reporting person mistakenly reported the number of shares of common stock beneficially owned following the reported transaction as 91,986 in the original Form 4.  Following the reported transaction, the reporting person owned only 90,986 shares of common stock.</footnote>
        <footnote id="F4">The reporting person originally reported this transaction on a Form 4 filed on March 16, 2006.  The reporting person mistakenly reported the number of underlying shares of common stock in the reported transaction as 11,000 in the original Form 4.  The correct number of underlying shares of common stock in the reported transaction was 11,500.</footnote>
        <footnote id="F5">Vests in equal annual installments over a 4 year period, commencing one year after this option has been granted.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Richard E Davis</signatureName>
        <signatureDate>2006-03-21</signatureDate>
    </ownerSignature>
</ownershipDocument>
