<?xml version="1.0"?>
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    <documentType>4</documentType>

    <periodOfReport>2012-10-01</periodOfReport>

    <issuer>
        <issuerCik>0000740260</issuerCik>
        <issuerName>VENTAS INC</issuerName>
        <issuerTradingSymbol>VTR</issuerTradingSymbol>
    </issuer>

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            <rptOwnerCik>0001195500</rptOwnerCik>
            <rptOwnerName>CROCKER DOUGLAS II</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>71 SOUTH WACKER DRIVE, SUITE 3400</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>CHICAGO,</rptOwnerCity>
            <rptOwnerState>IL</rptOwnerState>
            <rptOwnerZipCode>60606</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
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            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

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                <value>Common Stock</value>
            </securityTitle>
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            </transactionDate>
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                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
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            <transactionAmounts>
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                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
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                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
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                </transactionAcquiredDisposedCode>
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                <transactionPricePerShare>
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            <transactionDate>
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                <transactionCode>M</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
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                <transactionPricePerShare>
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                <transactionAcquiredDisposedCode>
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                    <value></value>
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        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
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            <transactionDate>
                <value>2012-10-03</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F3"/>
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            <transactionAmounts>
                <transactionShares>
                    <value>20000</value>
                </transactionShares>
                <transactionPricePerShare>
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                </transactionPricePerShare>
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                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Stock Option (Right to Buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>22.15</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2012-10-03</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>M</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>5000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2004-01-05</value>
                <footnoteId id="F4"/>
            </exerciseDate>
            <expirationDate>
                <value>2014-01-05</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>5000</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>40000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeTransaction>
        <derivativeTransaction>
            <securityTitle>
                <value>Stock Option (Right to Buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>27.09</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2012-10-03</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>M</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
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                </transactionShares>
                <transactionPricePerShare>
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                <transactionAcquiredDisposedCode>
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                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2005-01-03</value>
                <footnoteId id="F5"/>
            </exerciseDate>
            <expirationDate>
                <value>2015-01-03</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>5000</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>35000</value>
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                    <value>D</value>
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        </derivativeTransaction>
        <derivativeTransaction>
            <securityTitle>
                <value>Stock Option (Right to Buy)</value>
            </securityTitle>
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            <transactionDate>
                <value>2012-10-03</value>
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                <transactionFormType>4</transactionFormType>
                <transactionCode>M</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>5000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
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                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2006-01-01</value>
                <footnoteId id="F6"/>
            </exerciseDate>
            <expirationDate>
                <value>2016-01-01</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>5000</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
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                <sharesOwnedFollowingTransaction>
                    <value>30000</value>
                </sharesOwnedFollowingTransaction>
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            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeTransaction>
        <derivativeTransaction>
            <securityTitle>
                <value>Stock Option (Right to Buy)</value>
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            <conversionOrExercisePrice>
                <value>33.57</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2012-10-03</value>
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            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>M</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
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            <transactionAmounts>
                <transactionShares>
                    <value>5000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
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                <transactionAcquiredDisposedCode>
                    <value>D</value>
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            <exerciseDate>
                <value>2009-01-01</value>
                <footnoteId id="F7"/>
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            <expirationDate>
                <value>2019-01-01</value>
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            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
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                <underlyingSecurityShares>
                    <value>5000</value>
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                    <footnoteId id="F8"/>
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                <directOrIndirectOwnership>
                    <value>D</value>
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                <natureOfOwnership>
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        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Common stock in the form of units granted under the Ventas Nonemployee Directors' Deferred Stock Compensation Plan (the &quot;Plan&quot;) in lieu of director fees pursuant to the director's deferral election.  Such units are payable solely in common stock and subject to the terms and conditions of the director's deferral election and the Plan.</footnote>
        <footnote id="F2">Includes 229.370 units acquired on September 28, 2012, under the Plan as a result of dividend equivalents credited with respect to the dividend on Issuer's common stock paid on September 28, 2012.</footnote>
        <footnote id="F3">On October 3, 2012, the Reporting Person transmitted to the Securities and Exchange Commission (the &quot;SEC&quot;) a Form 144 covering the sale of the Issuer's common stock reported in Table I.  The price reported in column 4 is a weighted average price. These shares were sold by the Reporting Person in multiple transactions at prices ranging from $62.86 to $63.02, inclusive.  The Reporting Person undertakes to provide Issuer, any security holder of Issuer or the staff of the SEC, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote (3).</footnote>
        <footnote id="F4">These options were part of a previously reported grant of 5,000 on January 5, 2004, by the Issuer to the Reporting Person that vested in two equal annual installments beginning on January 5, 2004.</footnote>
        <footnote id="F5">These options were part of a previously reported grant of 5,000 on January 3, 2005, by the Issuer to the Reporting Person that vested in two equal annual installments beginning on January 3, 2005.</footnote>
        <footnote id="F6">These options were part of a previously reported grant of 5,000 on January 1, 2006, by the Issuer to the Reporting Person that vested in two equal annual installments beginning on January 1, 2006.</footnote>
        <footnote id="F7">These options were part of a previously reported grant of 5,000 on January 1, 2009, by the Issuer to the Reporting Person that vested in two equal annual installments beginning on January 1, 2009.</footnote>
        <footnote id="F8">Represents total number of unexercised stock options held by the Reporting Person as of October 3, 2012.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Douglas Crocker, II, By: T. Richard Riney, Attorney-in-Fact</signatureName>
        <signatureDate>2012-10-03</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0306
4
2012-10-01
0000740260
VENTAS INC
VTR
0001195500
CROCKER DOUGLAS II
71 SOUTH WACKER DRIVE, SUITE 3400
CHICAGO,
IL
60606
1
0
0
0
Common Stock
2012-10-01
4
A
0
465.06
61.82
A
79107.247
D
Common Stock
2012-10-03
4
M
0
5000
22.15
A
84107.247
D
Common Stock
2012-10-03
4
M
0
5000
27.09
A
89107.247
D
Common Stock
2012-10-03
4
M
0
5000
32.02
A
94107.247
D
Common Stock
2012-10-03
4
M
0
5000
33.57
A
99107.247
D
Common Stock
2012-10-03
4
S
0
20000
62.9494
D
79107.247
D
Stock Option (Right to Buy)
22.15
2012-10-03
4
M
0
5000
0
D
2004-01-05
2014-01-05
Common Stock
5000
40000
D
Stock Option (Right to Buy)
27.09
2012-10-03
4
M
0
5000
0
D
2005-01-03
2015-01-03
Common Stock
5000
35000
D
Stock Option (Right to Buy)
32.02
2012-10-03
4
M
0
5000
0
D
2006-01-01
2016-01-01
Common Stock
5000
30000
D
Stock Option (Right to Buy)
33.57
2012-10-03
4
M
0
5000
0
D
2009-01-01
2019-01-01
Common Stock
5000
25000
D
Common stock in the form of units granted under the Ventas Nonemployee Directors' Deferred Stock Compensation Plan (the "Plan") in lieu of director fees pursuant to the director's deferral election.  Such units are payable solely in common stock and subject to the terms and conditions of the director's deferral election and the Plan.
Includes 229.370 units acquired on September 28, 2012, under the Plan as a result of dividend equivalents credited with respect to the dividend on Issuer's common stock paid on September 28, 2012.
On October 3, 2012, the Reporting Person transmitted to the Securities and Exchange Commission (the "SEC") a Form 144 covering the sale of the Issuer's common stock reported in Table I.  The price reported in column 4 is a weighted average price. These shares were sold by the Reporting Person in multiple transactions at prices ranging from $62.86 to $63.02, inclusive.  The Reporting Person undertakes to provide Issuer, any security holder of Issuer or the staff of the SEC, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote (3).
These options were part of a previously reported grant of 5,000 on January 5, 2004, by the Issuer to the Reporting Person that vested in two equal annual installments beginning on January 5, 2004.
These options were part of a previously reported grant of 5,000 on January 3, 2005, by the Issuer to the Reporting Person that vested in two equal annual installments beginning on January 3, 2005.
These options were part of a previously reported grant of 5,000 on January 1, 2006, by the Issuer to the Reporting Person that vested in two equal annual installments beginning on January 1, 2006.
These options were part of a previously reported grant of 5,000 on January 1, 2009, by the Issuer to the Reporting Person that vested in two equal annual installments beginning on January 1, 2009.
Represents total number of unexercised stock options held by the Reporting Person as of October 3, 2012.
Douglas Crocker, II, By: T. Richard Riney, Attorney-in-Fact
2012-10-03