<PAGE>
                                                                  Exhibit 10.6.4

                                 PROMISSORY NOTE


$30,000                                                      As of July 26, 2005
                                                              New York, New York


             Healthcare Acquisition Corp. (the "Maker") promises to pay to the
order of John Pappajohn (the "Payee") the principal sum of Thirty Thousand
Dollars and No Cents ($30,000) in lawful money of the United States of America,
on the terms and conditions described below.

     1. PRINCIPAL. The principal balance of this Note shall be repayable on the
earlier of (i) April 28, 2006 or (ii) the date on which Maker consummates an
initial public offering of its securities.

     2. INTEREST. No interest shall accrue on the unpaid principal balance of
this Note.

     3. APPLICATION OF PAYMENTS. All payments shall be applied first to payment
in full of any costs incurred in the collection of any sum due under this Note,
including (without limitation) reasonable attorney's fees, then to the payment
in full of any late charges and finally to the reduction of the unpaid principal
balance of this Note.

     4. EVENTS OF DEFAULT. The following shall constitute Events of Default:

         (a) Failure to Make Required Payments. Failure by Maker to pay the
principal of this Note within five (5) business days following the date when
due.

         (b) Voluntary Bankruptcy, Etc. The commencement by Maker of a voluntary
case under the Federal Bankruptcy Code, as now constituted or hereafter amended,
or any other applicable federal or state bankruptcy, insolvency, reorganization,
rehabilitation or other similar law, or the consent by it to the appointment of
or taking possession by a receiver, liquidator, assignee, trustee, custodian,
sequestrator (or other similar official) of Maker or for any substantial part of
its property, or the making by it of any assignment for the benefit of
creditors, or the failure of Maker generally to pay its debts as such debts
become due, or the taking of corporate action by Maker in furtherance of any of
the foregoing.

         (c) Involuntary Bankruptcy, Etc. The entry of a decree or order for
relief by a court having jurisdiction in the premises in respect of Maker in an
involuntary case under the Federal Bankruptcy Code, as now or hereafter
constituted, or any other applicable federal or state bankruptcy, insolvency or
other similar law, or appointing a receiver, liquidator, assignee, custodian,
trustee, sequestrator (or similar official) of Maker or for any substantial part
of its property, or ordering the winding-up or liquidation of its affairs, and
the continuance of any such decree or order unstayed and in effect for a period
of 60 consecutive days.
<PAGE>

     5. REMEDIES.

         (a) Upon the occurrence of an Event of Default specified in Section
4(a), Payee may, by written notice to Maker, declare this Note to be due and
payable, whereupon the principal amount of this Note, and all other amounts
payable thereunder, shall become immediately due and payable without
presentment, demand, protest or other notice of any kind, all of which are
hereby expressly waived, anything contained herein or in the documents
evidencing the same to the contrary notwithstanding.

         (b) Upon the occurrence of an Event of Default specified in Sections
4(b) and 4(c), the unpaid principal balance of, and all other sums payable with
regard to, this Note shall automatically and immediately become due and payable,
in all cases without any action on the part of Payee.

     6. WAIVERS. Maker and all endorsers and guarantors of, and sureties for,
this Note waive presentment for payment, demand, notice of dishonor, protest,
and notice of protest with regard to the Note, all errors, defects and
imperfections in any proceedings instituted by Payee under the terms of this
Note, and all benefits that might accrue to Maker by virtue of any present or
future laws exempting any property, real or personal, or any part of the
proceeds arising from any sale of any such property, from attachment, levy or
sale under execution, or providing for any stay of execution, exemption from
civil process, or extension of time for payment; and Maker agrees that any real
estate that may be levied upon pursuant to a judgment obtained by virtue hereof,
on any writ of execution issued hereon, may be sold upon any such writ in whole
or in part in any order desired by Payee.

     7. UNCONDITIONAL LIABILITY. Maker hereby waives all notices in connection
with the delivery, acceptance, performance, default, or enforcement of the
payment of this Note, and agrees that its liability shall be unconditional,
without regard to the liability of any other party, and shall not be affected in
any manner by any indulgence, extension of time, renewal, waiver or modification
granted or consented to by Payee, and consents to any and all extensions of
time, renewals, waivers, or modifications that may be granted by Payee with
respect to the payment or other provisions of this Note, and agree that
additional makers, endorsers, guarantors, or sureties may become parties hereto
without notice to them or affecting their liability hereunder.

     8. NOTICES. Any notice called for hereunder shall be deemed properly given
if (i) sent by certified mail, return receipt requested, (ii) personally
delivered, (iii) dispatched by any form of private or governmental express mail
or delivery service providing receipted delivery or (iv) sent by telefacsimile
or (v) to the following addresses or to such other address as either party may
designate by notice in accordance with this Section:

<PAGE>



     If to Maker:

             Healthcare Acquisition Corp.
             Attn: Derace L. Schaffer, M.D.
             2116 Financial Center
             666 Walnut Street
             Des Moines, Iowa  50309
             Fax: (515) 244-2346

     If to Payee:

             Matthew P. Kinley
             c/o Equity Dynamics
             2116 Financial Center
             666 Walnut Street
             Des Moines, Iowa  50309
             Fax: (515) 244-2346

            Notice shall be deemed given on the earlier of (i) actual receipt by
the receiving party, (ii) the date shown on a telefacsimile transmission
confirmation, (iii) the date reflected on a signed delivery receipt, or (iv) two
(2) Business Days following tender of delivery or dispatch by express mail or
delivery service.

     9. CONSTRUCTION. THIS NOTE SHALL BE CONSTRUED AND ENFORCED IN ACCORDANCE
WITH THE DOMESTIC, INTERNAL LAW, BUT NOT THE LAW OF CONFLICT OF LAWS, OF THE
STATE OF IOWA.

     10. SEVERABILITY. Any provision contained in this Note which is prohibited
or unenforceable in any jurisdiction shall, as to such jurisdiction, be
ineffective to the extent of such prohibition or unenforceability without
invalidating the remaining provisions hereof, and any such prohibition or
unenforceability in any jurisdiction shall not invalidate or render
unenforceable such provision in any other jurisdiction.

            IN WITNESS WHEREOF, Maker, intending to be legally bound hereby, has
caused this Note to be duly executed by its President the day and year first
above written.


                                             HEALTHCARE ACQUISITION CORP.


                                             By: /s/ Matthew P. Kinley
                                             ----------------------------------
                                             Name:  Matthew P. Kinley
                                             Title: President