<PAGE>   1


                                                                    EXHIBIT 10.4


                              THIRD LEASE AMENDMENT

         THIS THIRD LEASE AMENDMENT (the "Amendment") is executed this 23rd day
of August, 2000, by and between DUKE-WEEKS REALTY LIMITED PARTNERSHIP, an
Indiana limited partnership ("Landlord"), and VASCULAR SOLUTIONS, INC., a
Minnesota corporation ("Tenant").

                              W I T N E S S E T H :
                              - - - - - - - - - - -

         WHEREAS, Massachusetts Mutual Life Insurance Company, as predecessor in
interest to Landlord (formerly known as Duke Realty Limited Partnership), and
Tenant entered into a certain lease dated February 11, 1998 as amended June 9,
1999 and October 24, 1999 (collectively the "Lease"), whereby Tenant leased from
Landlord certain premises consisting of approximately 16,743 rentable square
feet of space (the "Original Premises")and approximately 7,248 rentable square
feet of space (the "Additional Space") for a total of approximately 23,991
rentable square feet located in an office/warehouse building commonly known as
Plymouth Office/Tech Center, 2495 Xenium Lane North, Plymouth, Minnesota 55441;

         WHEREAS, Landlord and Tenant desire to expand the Original Premises and
Additional Space by approximately 4,833 rentable square feet (the "Second
Additional Space"). Collectively, the Original Premises, Additional Space and
Second Additional Space shall hereinafter be referred to as the "Premises"; and

         WHEREAS, Landlord and Tenant desire to amend certain provisions of the
Lease to reflect such expansion;

         NOW, THEREFORE, in consideration of the foregoing premises, the mutual
covenants herein contained and each act performed hereunder by the parties,
Landlord and Tenant hereby enter into this Amendment.

         1. Incorporation of Recitals. The above recitals are hereby
incorporated into this Amendment as if fully set forth herein.

         2. Amendment of Cover Page to Lease. Commencing September 1, 2000, the
cover page of the Lease is hereby amended as follows:

         Occupancy:        Reference to Base Rent "at the rate of $7,936.64 per
                           month" is deleted and replaced with "at the rate
                           identified in Third Amended Exhibit F".

         Base              Rent: See Third Amended Exhibit F, payable in advance
                           on or before the 1st day of each month during the
                           Lease Term at NW 7210, P.O. Box 1450, Minneapolis,
                           Minnesota 55485-7210, or such other place as Landlord
                           may from time to time designate in writing.

         Premises:         The space cross-hatched on Second Amended Exhibit B
                           attached hereto (the "Premises") consisting of
                           approximately 28,824 rentable square feet in the
                           building (the "Building") constructed on the tract of
                           land (the "Land") located in the City of Plymouth,
                           County of Hennepin, State of Minnesota (the "Land").

         3. Amendment of Section 2. Acceptance of Premises. Section 2 of the
Lease is hereby amended by adding the following:

         Tenant has personally inspected the Second Additional Space and accepts
         the same "as is" without representation or warranty by Landlord of any
         kind and with the understanding that Landlord shall have no
         responsibility with respect thereto except to construct in a good and
         workmanlike manner the improvements designated as Landlord's
         obligations as per mutually agreed upon plans and specifications and
         which shall be attached hereto as Second Amended Exhibit E. Tenant has
         personally inspected the Leased Premises and accepts the same "AS-IS"
         without representation or warranty by Landlord of any kind and with the
         understanding that Landlord shall have no responsibility with respect
         thereto, except Landlord shall provide an allowance for the direct
         costs of tenant finish improvements to the Leased Premises in an amount
         up to Nine Thousand Dollars ($9,000.00) (the "Allowance") to be used by
         Tenant prior to the Commencement Date. The Allowance shall be used
         exclusively to construct and pay for the tenant finish improvements set
         forth in Exhibit B (the "TFI"), that are directly related to the
         construction of the Leased Premises. Tenant shall reimburse Landlord
         for any cost or expense attributable to the tenant finish improvements
         which exceed the Allowance no later than thirty (30) days after receipt
         of an invoice from Landlord for such costs or expenses. Any Allowance
         not used by Tenant prior to the Commencement Date shall be forfeited by
         Tenant. Such tenant




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         finish improvement work shall be performed at Tenant's sole cost and
         expense and in accordance with plans and specifications prepared at
         Tenant's sole cost, which shall be reasonably agreed upon by both
         Landlord and Tenant upon prior to the commencement of the TFI. Tenant
         shall perform the TFI work in a good and workmanlike manner, in
         accordance with all applicable laws, regulations and building codes and
         Landlord's approvals which shall not be unreasonably withheld or
         delayed. The parties agree that it shall not be unreasonable for
         Landlord to withhold approval if, in Landlord's reasonable opinion, the
         proposed TFI plans and specifications do not match the existing
         architectural design and style of the Building or the proposed
         materials are not of equal or greater quality than existing Building
         standard. Landlord shall have the right to approve Tenant's contractor
         and all subcontractors performing such work, taking into consideration
         the quality of work and timeliness of performance. Tenant shall pay
         Landlord a fee for its supervision of the project, including review and
         approval of space plans and construction documents, equal to three
         percent (3%) of the total project cost. Within two business days of
         Tenant's receipt thereof, Tenant shall forward all invoices for TFI
         from contractors and subcontractors for the TFI to Landlord for payment
         from the Allowance and Landlord shall promptly process such invoices
         for payment until the amount of the Allowance is exhausted. Thereafter
         the payment of such bills and charges shall be Tenant's sole liability.
         The Tenant shall provide Landlord with copies of as-built plans and
         specifications upon completion of the TFI. No person shall be entitled
         to any lien derived through or under Tenant for any labor or material
         furnished to the Leased Premises, and nothing in this Lease shall be
         construed to constitute a consent by Landlord to the creation of any
         lien. If any lien is filed against the Leased Premises for work claimed
         to have been done for or material claimed to have been furnished to
         Tenant, Tenant shall cause such lien to be discharged of record within
         thirty (30) days after filing. Tenant shall indemnify Landlord from all
         costs, losses, expenses and attorneys' fees in connection with any
         construction or alteration and any related lien. Tenant agrees that all
         work on the initial and any subsequent tenant finish improvements shall
         be performed by Duke Construction Limited Partnership or a subsidiary
         or affiliate of Landlord ("Duke") which shall receive a construction
         management fee as Landlord's construction manager or general
         contractor.

         4. Amendment of Exhibit G. Tenant's Right to Early Termination.
Tenant's Right to Early Termination is hereby amended as follows:

         Provided Tenant is not in default, effective January 1, 2002 and every
         six (6) months thereafter, Tenant shall have the right to terminate
         this Lease by providing Landlord with six (6) months' prior written
         notice and as a condition of Tenant's termination, paying to Landlord
         as a termination fee in available bank funds, the sum of the following
         items (i) one month's gross rent based on monthly billing at the time
         notice is given; plus (ii) the unamortized portion of the leasing
         commissions in the amount of Thirty-six Thousand Five Hundred
         Eighty-four Dollars and Fifty-eight Cents ($36,584.58) paid by Landlord
         to United Properties Corporation in connection with the Lease; plus
         (iii) the unamortized portion of the leasing commissions in connection
         with the First Lease Amendment in the amount of Two Thousand Five
         Hundred Forty-nine Dollars and Seventy-three Cents ($2,549.73); plus
         (iv) the unamortized cost of the tenant finish improvements in the
         amount of Five Thousand Dollars ($5,000.00) (without consideration of
         any salvage value) made by Landlord pursuant to the Lease; (v) the
         unamortized cost of the tenant finish improvements of in the amount of
         Seven Thousand Two Hundred Forty-eight Dollars ($7,248.00) for the
         Additional Space; and (vi) the unamortized cost of the tenant finish
         improvements in the amount of Thirteen Thousand Three Hundred Six and
         00/100 Dollars ($13,306.00) as of the Termination Date. The
         amortization of the total costs as set forth above will be on a
         straight-line basis, using an eleven percent (11%) interest rate over
         the initial sixty (60) month term of the Lease with respect to subparts
         (ii) and (iv) and over the balance of the Lease Term remaining with
         respect to subparts (iii) and (v). See Amended Exhibit H for the
         amortization schedule.

         5. Tenant's Representations and Warranties. The undersigned represents
and warrants to Landlord that (i) Tenant is duly organized, validly existing and
in good standing in accordance with the laws of the state under which it was
organized; (ii) all action necessary to authorize the execution of this
Amendment has been taken by Tenant; and (iii) the individual executing and
delivering this Amendment on behalf of Tenant has been authorized to do so, and
such execution and delivery shall bind Tenant. Tenant, at Landlord's request,
shall provide Landlord with evidence of such authority.

         6. Examination of Amendment. Submission of this instrument for
examination or signature to Tenant does not constitute a reservation or option,
and it is not effective until execution by and delivery to both Landlord and
Tenant.

         7. Definitions. Except as otherwise provided herein, the capitalized
terms used in this Amendment shall have the definitions set forth in the Lease.



                                      -2-
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         8. Incorporation. This Amendment shall be incorporated into and made a
part of the Lease, and all provisions of the Lease not expressly modified or
amended hereby shall remain in full force and effect.

         IN WITNESS WHEREOF, the parties have caused this Amendment to be
executed on the day and year first written above.

                                       LANDLORD:

                                       DUKE-WEEKS REALTY LIMITED PARTNERSHIP,
                                       an Indiana limited partnership

                                       By: Duke-Weeks Realty Corporation,
                                           its general partner

                                       By: /s/ James W. Gray
                                          --------------------------------------
                                           James W. Gray
                                           Senior Vice President
                                           Minneapolis Industrial

                                       TENANT:

                                       VASCULAR SOLUTIONS, INC.,
                                       a Minnesota corporation

                                       By: /s/ Rick Buchholz
                                          --------------------------------------

                                       Printed: Rick Buchholz
                                               ---------------------------------

                                       Title: Treasurer
                                             -----------------------------------

STATE OF Minnesota      )
                        )   SS:
COUNTY OF Hennepin      )

         Before me, a Notary Public in and for said County and State, personally
appeared Rick Buchholz, by me known and by me known to be the Treasurer of
Vascular Solutions, Inc., a Minnesota corporation, who acknowledged the
execution of the foregoing "Third Lease Amendment" on behalf of said
corporation.

         WITNESS my hand and Notarial Seal this 23rd day of August, 2000.

                                       /s/ Charlene F. Cohodes
                                       -----------------------------------------
                                       Notary Public

                                       Charlene F. Cohodes
                                       -----------------------------------------
                                       (Printed Signature)


My Commission Expires: 1/31/05
                      --------------

My County of Residence: Hennepin
                       -------------





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                             THIRD AMENDED EXHIBIT F

                               Base Rent Schedule


Original Premises:

         Term                                        Monthly Base Rent
         ----                                        -----------------

         04/01/98 - 03/31/00                         $7,935.64
         04/01/00 - 03/31/03                         $8,340.26

Additional Space:

         Term                                        Monthly Base Rent
         ----                                        -----------------

         07/01/99 - 04/30/01                         $4,097.17
         05/01/01 - 03/31/03                         $4,299.01

Second Additional Space:

         Term                                        Monthly Base Rent
         ----                                        -----------------

         9/1/00 - 3/31/03                            $3,318.66