Exhibit 10.4

FIRST AMENDMENT TO

AGREEMENT AND PLAN OF MERGER

This AMENDMENT TO AGREEMENT AND PLAN OF MERGER (this “Amendment”), dated
effective as of May 21, 2012, is by and among USMD Holdings, Inc., a Delaware
corporation, UANT Ventures, L.L.P., a Texas limited liability partnership, UANT
Acquisition Company, Inc., a Texas corporation and a wholly-owned subsidiary of
Ventures and The Medical Clinic of North Texas P.A., a Texas professional
association.

WHEREAS, the Parties previously entered into that certain Agreement and Plan of
Merger dated December 1, 2011 (the “Agreement”); and

WHEREAS, the Parties desire to amend certain terms of the Agreement as set forth
herein.

NOW, THEREFORE, in consideration of the mutual agreements, provisions and
covenants contained herein, and for other good and valuable consideration, the
receipt and sufficiency of which are hereby acknowledged, the Parties hereto
agree as follows:

ARTICLE I

DEFINITIONS

Capitalized terms used but not defined herein shall have the meanings ascribed
to them in the Agreement.

ARTICLE II

AMENDMENTS; GENERAL

2.1 Section 1.4 of the Agreement is hereby deleted in its entirety and replaced
with the following, effective as of the date hereof:

1.4 Merger Consideration.

(a) Subject to the adjustments set forth in Section 1.4(c) herein, the
consideration payable by Ventures to the MCNT Holders (the “Merger
Consideration”) shall be paid by Ventures at Closing to such holders in the form
of Class C Partnership Interests in Ventures (the “Class C Interests”)
equivalent in value to each such MCNT Holder’s pro rata percentage set forth on
Schedule 1.4(a) of the “Adjusted Equity Value” of MCNT set forth in Cell Q69 of
Schedule 1.41; provided, that the Parties agree and acknowledge that no such
consideration shall be paid by Ventures to any holder of Dissenting Shares, it
being agreed that such holder shall receive consideration in exchange for his or
her Dissenting Shares as set forth in Section 1.3(c) above and any MCNT Holders
who are not holders of Dissenting Shares shall not, by virtue of there being any
Dissenting Shares, be entitled to receive more than their pro rata percentage
set forth on Schedule 1.4(a) of the “Adjusted Equity Value” of MCNT set forth in
Cell Q69 of Schedule 1.41.

(b) The Merger Consideration payable hereunder has been derived from the
relative fair market values of the businesses of MCNT, Impel, UANT and USMD as
determined by fair market value appraisals (and updates to the same) conducted
by experienced and independent third party appraisal companies.

(c) The aggregate Merger Consideration payable at Closing shall be adjusted
following the Closing based upon changes in the Adjusted Equity Value of MCNT

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relative to, (i) changes in the Adjusted Equity Value of Impel, (ii) changes in
the Adjusted Equity Value of UANT, (iii) changes in the Adjusted Equity Value of
Ventures, and (iv) changes in the Adjusted Equity Value of the shares of common
stock of USMD contributed to Ventures by USMD shareholders pursuant to the UANT
Agreement, in each case between September 30, 2011 and 11:59 p.m. local time in
Dallas, Texas on the Closing Date (the “Schedule 1.41 Adjustments”). The
Schedule 1.41 Adjustments shall be calculated as follows:

(i) to reflect any changes from December 31, 2011 in “Total Subsidiary Level
Debt,” “USMD Corporate Level Debt,” “Ventures/UANT Corporate Level Debt,” “Impel
Level Debt,” and “MCNT Corporate Level Debt,” as set forth in Columns D, F, G,
H, and I, respectively, of Schedule 1.41;

(ii) to reflect any changes since September 30, 2011 in ownership percentages of
the assets or investments held by either USMD, Ventures/UANT, Impel, and MCNT,
as reflected in Columns J, L, N, and P, respectively, of Schedule 1.41;

(iii) to reflect on Schedule 1.41 the amount of any “Deferred Payment
Obligations” of USMD, Ventures/UANT, Impel, and MCNT as set forth in Cells K62,
M62, O62, and Q62, respectively. Such amounts shall be calculated in accordance
with the Schedule 1.41 Deferred Payment Obligations as defined in Article IX;

(iv) to reflect the amount of any “Net Working Capital Adjustments” of USMD,
Ventures/UANT, Impel, and MCNT in Cells D75 of Schedule 1.42, D68 of Schedule
1.43, D75 of Schedule 1.44, and D75 of Schedule 1.45, respectively; and

(v) to reflect on Schedule 1.41 the amount of any mutually approved capital
expenditures (A) since December 31, 2010 relating to fixed assets of the UANT
clinical practice and (B) since September 30, 2011 relating to fixed assets or
mutually approved capital contributions of USMD, Ventures/UANT, Impel, and MCNT
as set forth in Cells K65, M65, O65, and Q65, including without limitation
approved capital expenditures for equipment, building or tenant improvements.

(d) For the purposes of computing the adjustments, if any, pursuant to
subsection (c) above, no adjustments to the Merger Consideration or Adjusted
Equity Values reflected on Row 69 of Schedule 1.41 shall be made to the extent
of any amounts already included in the calculations set forth in Rows 62-65 and
Row 67 of Schedule 1.41 and the following provisions shall be applicable:

(i) No later than forty-five (45) days following the Closing Date, the MCNT
Representative shall prepare and deliver to Ventures a calculation of the
Schedule 1.41 Adjustments related to MCNT, based upon its financial statements
at and as of the Closing. No later than fifteen (15) days following the delivery
by the MCNT Representative of the proposed Schedule 1.41 Adjustments related to
MCNT, Ventures shall deliver to the MCNT Representative a calculation of all
Schedule 1.41 Adjustments set forth in subsection (c) above. Each of the MCNT
Representative and Ventures shall give to the other any information and back-up
materials reasonably requested by the requesting Party with respect to the
Schedule 1.41 Adjustments.

(ii) The MCNT Representative shall have thirty (30) days following receipt of
the calculations of Schedule 1.41 Adjustments to notify Ventures of any dispute
of any item contained therein, which notice shall set forth in reasonable detail
the basis for such dispute. At any time within such thirty (30)-day period, the
MCNT Representative shall be entitled to agree with any or all of the items set
forth in Ventures’s calculation of the Schedule 1.41 Adjustments.

 

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(iii) If the MCNT Representative does not notify Ventures of any such dispute
within such thirty (30)-day period, or notifies Ventures of its agreement with
Ventures’s calculations, Ventures’s calculations of the Schedule 1.41
Adjustments shall be final and binding on the Parties and shall be deemed to be
final and binding for purposes of any adjustments to consideration made pursuant
to the UANT Agreement.

(iv) If the MCNT Representative notifies Ventures of any such dispute within
such thirty (30)-day period, the Schedule 1.41 Adjustments shall be resolved as
follows:

(A) The MCNT Representative and Ventures shall jointly determine the extent of
any Schedule 1.41 Adjustments as promptly as practicable.

(B) In the event that the MCNT Representative and Ventures are unable to agree
upon any of the Schedule 1.41 Adjustments, the Parties shall submit such matter
to the Dallas, Texas office of Grant Thornton LLP (or if such firm is unwilling
or unable to serve, another nationally recognizable accounting firm mutually
agreed upon by the Parties), who shall make the final determination with respect
to the correctness of the proposed Schedule 1.41 Adjustments in light of the
terms and provisions of this Agreement, with such determination being final and
binding on the Parties and be final and binding for purposes of any adjustments
to consideration made pursuant to the UANT Agreement.

2.2 All other references in the Agreement to “Schedule 1.4” shall be amended to
mean “Schedule 1.41” and all other references in the Agreement to the “Schedule
1.4 Adjustments” shall be amended to mean “Schedule 1.41 Adjustments.”

2.3 All references in the Agreement to the “MCNT Conversion” shall be amended to
mean the conversion of MCNT from a Texas professional association to a Texas
professional limited liability company.

2.4 Schedule 1.4(a) of the Agreement is hereby deleted in its entirety and
replaced with Schedule 1.4(a) attached hereto, effective as of the date hereof:

2.5 Schedule 2.4 of the Agreement is hereby deleted in its entirety and replaced
with Schedule 2.4 attached hereto, effective as of the date hereof:

2.6 Section 2.5 of the Agreement is hereby deleted in its entirety and replaced
with the following, effective as of the date hereof:

2.5 Litigation. Except as set forth on Schedule 2.5 hereto, as of the Disclosure
Schedule Date, there is no Action pending or, to MCNT’s Knowledge, threatened
against or affecting MCNT that (a) adversely affects or challenges the legality,
validity or enforceability of this Agreement or (b) could, if there were an
unfavorable decision, individually or in the aggregate, have or reasonably be
expected to result in a Material Adverse Effect for MCNT.

 

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2.7 Section 4.3 of the Agreement is hereby deleted in its entirety and replaced
with the following, effective as of the date hereof:

4.3 No Conflicts; Consents. The execution and delivery by Holdings of this
Agreement do not, and the consummation of the Transactions and compliance with
the terms hereof will not, conflict with, or result in any violation of or
default (with or without notice or lapse of time, or both) under, or give rise
to a right of termination, cancellation or acceleration of any obligation or to
loss of a material benefit under, or result in the creation of any Lien, other
than a Permitted Lien, upon any of the shares of common stock of Holdings or
properties or assets of Holdings under, any provision of (a) the Holdings
Constituent Instruments, (i) any Contract to which Holdings or any of its
properties or assets are subject, or (ii) any material Law applicable to
Holdings or its properties or assets or (b) require any consent, approval,
authorization or permit of, or filing with, or notification to, any Governmental
Entity.

2.7 The definition of “MCNT Conversion Documents” shall mean the certificate of
conversion, certificate of formation and company agreement of MCNT in effect
following the consummation of the MCNT Conversion, each as amended.

2.8 Section 4.4(a) and (b) of the Agreement are hereby deleted in their entirety
and replaced with the following, effective as of the date hereof:

(a) As of the date hereof, the authorized capital stock of Holdings consists of
1,000,000 shares of preferred stock, $0.01 par value, of which no shares are
issued and outstanding as of the date hereof, and 49,000,000 shares of common
stock of Holdings, par value $.01 (“Holdings Stock”), of which 35,800 are issued
and outstanding as of the date hereof. As of the date hereof, up to 964,200
shares of Holdings Stock are reserved for issuance under the Holdings Equity
Plan. Except as set forth above or in connection with the UANT/USMD
Contribution, no shares of capital stock or other voting securities of Holdings
are issued, reserved for issuance or outstanding.

(b) Immediately following the consummation of the Merger, the Impel Merger and
the UANT/USMD Contribution, (i) the authorized capital stock of Holdings shall
consists of 1,000,000 shares of preferred stock, $0.01 par value, of which no
shares shall be issued and outstanding as of the Closing Date, 49,000,000 shares
of Holdings Stock, of which 10,035,800 shares are expected to be issued and
outstanding as of the Closing Date and 964,200 shares shall be reserved for
issuance under the Holdings Equity Plan as of the Closing Date and (ii) the
capital structure of Holdings’ Subsidiaries shall be as set forth on Schedule
4.4(b) hereto. Schedule 4.4(b) sets forth (i) the name and jurisdiction of each
Subsidiary of Holdings immediately following the Closing, and (ii) a complete
and accurate list of all outstanding securities beneficially owned by Holdings
or its Subsidiaries immediately following Closing. Except as set forth above,
immediately following the consummation of the Merger, the Impel Merger and the
UANT/USMD Contribution, no shares of capital stock or other voting securities of
Holdings shall be issued, reserved for issuance or outstanding.

2.9 Other than the amendments and modifications specifically contained in this
Amendment, the Agreement remains in full force and effect.

2.10 This Amendment may be executed in one or more counterparts, all of which
shall be considered one and the same agreement and shall become effective when
one or more counterparts have been signed by each of the Parties and delivered
to the other Parties. Facsimile execution and delivery of this Amendment is
legal, valid and binding for all purposes.

 

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2.11 This Amendment shall be governed by, and construed in accordance with, the
laws of the State of Texas, regardless of the laws that might otherwise govern
under applicable principles of conflicts of laws thereof.

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IN WITNESS WHEREOF, the parties hereto have caused this Amendment to Agreement
and Plan of Merger to be duly executed by their respective authorized
signatories as of the date first indicated above.

 

HOLDINGS:

 

USMD Holdings, Inc., a Delaware

corporation

 

By:  

 

Name:   John House, M.D. Title:   Chairman and CEO

 

VENTURES:

 

UANT VENTURES, L.L.P. a Texas limited

liability partnership

 

By:  

 

Name:   Mark McCurdy, M.D. Title:   Authorized Partner

 

MERGER SUB:

 

UANT ACQUISITION COMPANY, Inc., a

Texas corporation

    By UANT Ventures, LLP

    Its Sole Member

 

By:  

 

Name:   Mark McCurdy, M.D. Title:   Authorized Partner

Signature Page to Amendment to Agreement and Plan of Merger

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MCNT:

 

THE MEDICAL CLINIC OF NORTH

TEXAS, a Texas professional association

 

By:  

 

Name:   Richard Johnston, M.D. Title:   President

Signature Page to Amendment to Agreement and Plan of Merger

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Schedule 1.4(a)

Merger Consideration

 

MCNT Holder

 

Shares of MCNT Stock Owned

 

Pro Rata Percentage of Class C

Partnership Interests to be

Received

Adams, Amy MD

  1   0.94%

Atkins, Baron MD

  1   0.94%

Auvenshine, Michael MD

  1   0.94%

Baker, Jeremy MD

  1   0.94%

Baker, Shannon MD

  1   0.94%

Barker, Thomas MD

  1   0.94%

Barton, Courtney MD

  1   0.94%

Bartos, Justin MD

  1   0.94%

Bates, Edward MD

  1   0.94%

Becerra, Oscar MD

  1   0.94%

Bindner, Stephen MD

  1   0.94%

Brock, Steven MD

  1   0.94%

Bucan-Kurepa, Jelena MD

  1   0.94%

Buschow, Robert MD

  1   0.94%

Carmichael, Kristen MD

  1   0.94%

Carnevale, Kristina MD

  1   0.94%

Cheng, Jung T MD

  1   0.94%

Childers, James MD

  1   0.94%

Chiniwala, Rupal MD

  1   0.94%

Clifford, Susan K MD

  1   0.94%

Conoley, Megan MD

  1   0.94%

Copeland, Stephanie MD

  1   0.94%

Cox Jr., Ralph, MD

  1   0.94%

Culver, Jennifer MD

  1   0.94%

Cummings, Fred MD

  1   0.94%

Dabelic, R. Kendra MD

  1   0.94%

Dalley, Albert MD

  1   0.94%

Dejecacion, Jodie MD

  1   0.94%

Demarie, Bryan MD

  1   0.94%

Dias, Keryn MD

  1   0.94%

Dickey, Russell MD

  1   0.94%

Dooley, Christina MD

  1   0.94%

Eldridge, Kevin MD

  1   0.94%

Eppstein, Roger MD

  1   0.94%

Fielder, Martin MD

  1   0.94%

Fikkert, Chimene MD

  1   0.94%

Finke, Mary MD

  1   0.94%

Freeman, John W MD

  1   0.94%

Gaddam, Madhavi MD

  1   0.94%

Gibson-Hull, Stacey MD

  1   0.94%

Godbey, Teresa MD

  1   0.94%

Godfrey, Mark MD

  1   0.94%

Gonzalez, Virginia MD

  1   0.94%

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Graham, Robert MD

  1   0.94%

Guthrie, William MD

  1   0.94%

Haq, Seema MD

  1   0.94%

Harris, Carolyn MD

  1   0.94%

Harris, Timothy MD

  1   0.94%

Hays, Brad MD

  1   0.94%

Hunter, David MD

  1   0.94%

Hutcheson, Richard MD

  1   0.94%

Isaacs, Emily MD

  1   0.94%

Jeffers, John MD

  1   0.94%

Johnson, Steven E MD

  1   0.94%

Johnston, Mark MD

  1   0.94%

Johnston, Richard MD

  1   0.94%

Jones, Carrie MD

  1   0.94%

Jones, Christina MD

  1   0.94%

Kallam, G. Byron MD

  1   0.94%

Kier, Carlos MD

  1   0.94%

Krombach, R. Stephen MD

  1   0.94%

Krum, Theodore MD

  1   0.94%

Lam, Van MD

  1   0.94%

Lehmann, Claudio MD

  1   0.94%

Lester, Lynn MD

  1   0.94%

Lorimer MD, Douglas D

  1   0.94%

Mace-Motta, Cynthia DO

  1   0.94%

Machos Jr., Robert MD

  1   0.94%

Martin, John R MD

  1   0.94%

Matthews, Edwin MD

  1   0.94%

Maust, Joel MD

  1   0.94%

McColm, Vincent MD

  1   0.94%

Mewis, Beth MD

  1   0.94%

Meyer, Carissa MD

  1   0.94%

Meyer, Matthew MD

  1   0.94%

Morrill, Audrey MD

  1   0.94%

Nelson Jr., Edward MD

  1   0.94%

Oei, Bing MD

  1   0.94%

Olivo, Julie MD

  1   0.94%

Parrill, Ellen MD

  1   0.94%

Pavey, Scott MD

  1   0.94%

Penny, Richard MD

  1   0.94%

Phipps, Lowell MD

  1   0.94%

Raja, Kalyani MD

  1   0.94%

Rathkamp, Quynh MD

  1   0.94%

Readinger, James MD

  1   0.94%

Reddy, Himabindu MD

  1   0.94%

Russell, David MD

  1   0.94%

Sanders, J. Paul MD

  1   0.94%

Shore, Kenneth MD

  1   0.94%

Smitherman, Robert Kent MD

  1   0.94%

So, Ashley Unwoo MD

  1   0.94%

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Speaks, Lynn DO

  1   0.94%

Strittmatter, Marla MD

  1   0.94%

Summakia, Mohammed MD

  1   0.94%

Talbot, Scott MD

  1   0.94%

Teng, Jay MD

  1   0.94%

Teng, Li Ray MD

  1   0.94%

Tran, Khang MD

  1   0.94%

Viktorin, Gina MD

  1   0.94%

Walker, Joel MD

  1   0.94%

Wallace, Erin Elizabeth MD

  1   0.94%

Walsh, Heather MD

  1   0.94%

Williams, Celeste DO

  1   0.94%

Wittenberg, John MD

  1   0.94%

Wood, John P MD

  1   0.94%

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Schedule 2.4

Capital Structure

 

MCNT Holder

 

Shares of MCNT Stock Owned

Adams, Amy MD

  1

Atkins, Baron MD

  1

Auvenshine, Michael MD

  1

Baker, Jeremy MD

  1

Baker, Shannon MD

  1

Barker, Thomas MD

  1

Barton, Courtney MD

  1

Bartos, Justin MD

  1

Bates, Edward MD

  1

Becerra, Oscar MD

  1

Bindner, Stephen MD

  1

Brock, Steven MD

  1

Bucan-Kurepa, Jelena MD

  1

Buschow, Robert MD

  1

Carmichael, Kristen MD

  1

Carnevale, Kristina MD

  1

Cheng, Jung T MD

  1

Childers, James MD

  1

Chiniwala, Rupal MD

  1

Clifford, Susan K MD

  1

Conoley, Megan MD

  1

Copeland, Stephanie MD

  1

Cox Jr., Ralph, MD

  1

Culver, Jennifer MD

  1

Cummings, Fred MD

  1

Dabelic, R. Kendra MD

  1

Dalley, Albert MD

  1

Dejecacion, Jodie MD

  1

Demarie, Bryan MD

  1

Dias, Keryn MD

  1

Dickey, Russell MD

  1

Dooley, Christina MD

  1

Eldridge, Kevin MD

  1

Eppstein, Roger MD

  1

Fielder, Martin MD

  1

Fikkert, Chimene MD

  1

Finke, Mary MD

  1

Freeman, John W MD

  1

Gaddam, Madhavi MD

  1

Gibson-Hull, Stacey MD

  1

Godbey, Teresa MD

  1

Godfrey, Mark MD

  1

Gonzalez, Virginia MD

  1

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Graham, Robert MD

  1

Guthrie, William MD

  1

Haq, Seema MD

  1

Harris, Carolyn MD

  1

Harris, Timothy MD

  1

Hays, Brad MD

  1

Hunter, David MD

  1

Hutcheson, Richard MD

  1

Isaacs, Emily MD

  1

Jeffers, John MD

  1

Johnson, Steven E MD

  1

Johnston, Mark MD

  1

Johnston, Richard MD

  1

Jones, Carrie MD

  1

Jones, Christina MD

  1

Kallam, G. Byron MD

  1

Kier, Carlos MD

  1

Krombach, R. Stephen MD

  1

Krum, Theodore MD

  1

Lam, Van MD

  1

Lehmann, Claudio MD

  1

Lester, Lynn MD

  1

Lorimer MD, Douglas D

  1

Mace-Motta, Cynthia DO

  1

Machos Jr., Robert MD

  1

Martin, John R MD

  1

Matthews, Edwin MD

  1

Maust, Joel MD

  1

McColm, Vincent MD

  1

Mewis, Beth MD

  1

Meyer, Carissa MD

  1

Meyer, Matthew MD

  1

Morrill, Audrey MD

  1

Nelson Jr., Edward MD

  1

Oei, Bing MD

  1

Olivo, Julie MD

  1

Parrill, Ellen MD

  1

Pavey, Scott MD

  1

Penny, Richard MD

  1

Phipps, Lowell MD

  1

Raja, Kalyani MD

  1

Rathkamp, Quynh MD

  1

Readinger, James MD

  1

Reddy, Himabindu MD

  1

Russell, David MD

  1

Sanders, J. Paul MD

  1

Shore, Kenneth MD

  1

Smitherman, Robert Kent MD

  1

So, Ashley Unwoo MD

  1

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Speaks, Lynn DO

  1

Strittmatter, Marla MD

  1

Summakia, Mohammed MD

  1

Talbot, Scott MD

  1

Teng, Jay MD

  1

Teng, Li Ray MD

  1

Tran, Khang MD

  1

Viktorin, Gina MD

  1

Walker, Joel MD

  1

Wallace, Erin Elizabeth MD

  1

Walsh, Heather MD

  1

Williams, Celeste DO

  1

Wittenberg, John MD

  1

Wood, John P MD

  1