-----BEGIN PRIVACY-ENHANCED MESSAGE-----
Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
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 TWSM7vrzLADbmYQaionwg5sDW3P6oaM5D3tdezXMm7z1T+B+twIDAQAB
MIC-Info: RSA-MD5,RSA,
 VvENDLXBQd96Upbam9Z4/fkwxpYiR1nB1SZeEYxN0AzMvrc96RU+m7eORB161IZM
 yGtves/FyjLAg7k3he6YMw==

<SEC-DOCUMENT>0000914190-10-000613.txt : 20100818
<SEC-HEADER>0000914190-10-000613.hdr.sgml : 20100818
<ACCEPTANCE-DATETIME>20100818123654
ACCESSION NUMBER:		0000914190-10-000613
CONFORMED SUBMISSION TYPE:	4/A
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20100813
FILED AS OF DATE:		20100818
DATE AS OF CHANGE:		20100818

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			Koehn Paul A
		CENTRAL INDEX KEY:			0001428164

	FILING VALUES:
		FORM TYPE:		4/A
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-52082
		FILM NUMBER:		101025038

	MAIL ADDRESS:	
		STREET 1:		651 CAMPUS DRIVE
		CITY:			ST PAUL
		STATE:			MN
		ZIP:			55112

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			Cardiovascular Systems Inc
		CENTRAL INDEX KEY:			0001180145
		STANDARD INDUSTRIAL CLASSIFICATION:	SURGICAL & MEDICAL INSTRUMENTS & APPARATUS [3841]
		IRS NUMBER:				411698056
		FISCAL YEAR END:			0630

	BUSINESS ADDRESS:	
		STREET 1:		651 CAMPUS DRIVE
		CITY:			ST. PAUL
		STATE:			MN
		ZIP:			55112
		BUSINESS PHONE:		651-259-1600

	MAIL ADDRESS:	
		STREET 1:		651 CAMPUS DRIVE
		CITY:			ST. PAUL
		STATE:			MN
		ZIP:			55112

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	REPLIDYNE INC
		DATE OF NAME CHANGE:	20020813
</SEC-HEADER>
<DOCUMENT>
<TYPE>4/A
<SEQUENCE>1
<FILENAME>edgar.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0303</schemaVersion>

    <documentType>4/A</documentType>

    <periodOfReport>2010-08-13</periodOfReport>

    <dateOfOriginalSubmission>2010-08-17</dateOfOriginalSubmission>

    <issuer>
        <issuerCik>0001180145</issuerCik>
        <issuerName>Cardiovascular Systems Inc</issuerName>
        <issuerTradingSymbol>CSII</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001428164</rptOwnerCik>
            <rptOwnerName>Koehn Paul A</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>651 CAMPUS DRIVE</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>ST. PAUL</rptOwnerCity>
            <rptOwnerState>MN</rptOwnerState>
            <rptOwnerZipCode>55112</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>VP of Manufacturing</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2010-08-13</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>35326</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>56221</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes></footnotes>

    <remarks>This Form 4/A is being filed solely for the purpose of correcting a clerical data entry error to reflect that the shares were acquired (and not disposed) on Table 1 in column 4.</remarks>

    <ownerSignature>
        <signatureName>/s/ John R. Remakel as Attorney-in-Fact for Paul Koehn pursuant to Power of Attorney previously filed.</signatureName>
        <signatureDate>2010-08-18</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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