FORM OF NOTE

Exhibit 4.3

FORM OF NOTE

THIS SECURITY AND THE OBLIGATIONS OF THE COMPANY (AS DEFINED HEREIN) AS EVIDENCED HEREBY (1) ARE NOT DEPOSITS WITH OR HELD BY THE COMPANY AND ARE NOT INSURED OR GUARANTEED BY ANY FEDERAL AGENCY OR INSTRUMENTALITY, INCLUDING, WITHOUT LIMITATION, THE FEDERAL DEPOSIT INSURANCE CORPORATION, AND (2) ARE SUBORDINATE IN THE RIGHT OF PAYMENT TO THE SENIOR INDEBTEDNESS (AS DEFINED IN THE INDENTURE IDENTIFIED HEREIN).

GLOBAL NOTE

THIS SECURITY IS A GLOBAL SECURITY WITHIN THE MEANING OF THE INDENTURE HEREINAFTER REFERRED TO AND IS REGISTERED IN THE NAME OF THE DEPOSITARY OR A NOMINEE THEREOF. THIS SECURITY MAY NOT BE EXCHANGED IN WHOLE OR IN PART FOR A SECURITY REGISTERED, AND NO TRANSFER OF THIS SECURITY IN WHOLE OR IN PART MAY BE REGISTERED IN THE NAME OF ANY PERSON OTHER THAN THE DEPOSITARY OR A NOMINEE THEREOF, EXCEPT IN THE LIMITED CIRCUMSTANCES DESCRIBED IN THE INDENTURE.

UNLESS AND UNTIL IT IS EXCHANGED IN WHOLE OR IN PART FOR THE INDIVIDUAL SECURITIES REPRESENTED HEREBY, THIS GLOBAL SECURITY MAY NOT BE TRANSFERRED EXCEPT AS A WHOLE (I) BY THE DEPOSITARY TO A NOMINEE OF THE DEPOSITARY OR (II) BY A NOMINEE OF THE DEPOSITARY OR THE DEPOSITARY TO A SUCCESSOR DEPOSITARY OR A NOMINEE OF SUCH SUCCESSOR DEPOSITARY. UNLESS THIS CERTIFICATE IS PRESENTED BY AN AUTHORIZED REPRESENTATIVE OF THE DEPOSITORY TRUST COMPANY TO THE ISSUER OR ITS AGENT FOR REGISTRATION OF TRANSFER, EXCHANGE OR PAYMENT AND ANY CERTIFICATE ISSUED IS REGISTERED IN THE NAME OF CEDE & CO. OR SUCH OTHER NAME AS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF THE DEPOSITORY TRUST COMPANY AND ANY PAYMENT IS MADE TO CEDE & CO., ANY TRANSFER, PLEDGE OR OTHER USE HEREOF FOR VALUE OR OTHERWISE BY OR TO ANY PERSON IS WRONGFUL SINCE THE REGISTERED OWNER HEREOF, CEDE & CO., HAS AN INTEREST HEREIN.

TRANSFERS OF THIS GLOBAL SECURITY SHALL BE LIMITED TO TRANSFERS IN WHOLE, BUT NOT IN PART, BY THE DEPOSITARY TO A NOMINEE OF THE DEPOSITARY, OR BY A NOMINEE OF THE DEPOSITARY TO THE DEPOSITARY OR ANOTHER NOMINEE OF THE DEPOSITARY, OR BY THE DEPOSITARY OR ANY SUCH NOMINEE TO A SUCCESSOR DEPOSITARY OR A NOMINEE OF SUCH SUCCESSOR DEPOSITARY

ENTERPRISE FINANCIAL SERVICES CORP

4.75% FIXED-TO-FLOATING RATE SUBORDINATED NOTE DUE NOVEMBER 1, 2026

CUSIP NO. 293712 AA3

ISIN NO. US293712AA32

Enterprise Financial Services Corp, a Delaware corporation (hereinafter called the “Company,” which term includes any successor corporation under the Indenture hereinafter referred to), for value received, hereby promises to pay to CEDE & CO., or its registered assigns, the principal sum of $50,000,000 (or such other amount as set forth in the Schedule of Increases or Decreases in Global Note attached hereto) on November 1, 2026 (such date is hereinafter referred to as the “Stated Maturity Date”), unless redeemed prior to such date, and to pay interest thereon (i) from, and including, November 1, 2016, to, but excluding, November 1, 2021, unless redeemed prior to such date, at a rate of 4.75% per annum, semi-annually in arrears on May 1 and November 1 of each year, commencing May 1, 2017 (each such date, a “Fixed Rate Interest Payment Date,” with the period from, and including, November 1, 2016 to, but excluding, the first Fixed Rate Interest Payment Date and each successive period from,

and including, a Fixed Rate Interest Payment Date to, but excluding, the next Fixed Rate Interest Payment Date being a “Fixed Rate Period”) and (ii) from, and including, November 1, 2021 to, but excluding, the Stated Maturity Date, unless redeemed subsequent to September 30, 2021 but prior to the Stated Maturity Date, at a rate equal to Three-month LIBOR, reset quarterly, plus 338.7 basis points (3.387%), payable quarterly in arrears on February 1, May 1, August 1, and November 1 of each year through the Stated Maturity Date or earlier redemption date (each, a “Floating Rate Interest Payment Date,” and together with the Fixed Rate Interest Payment Dates, the “Interest Payment Dates,” with the period from, and including, November 1, 2021 to, but excluding, the first Floating Rate Interest Payment Date and each successive period from, and including a Floating Rate Interest Payment Date to, but excluding, the next Floating Rate Interest Payment Date being a “Floating Rate Period”). The amount of interest payable on any Fixed Rate Interest Payment Date during the Fixed Rate Period will be computed on the basis of a 360-day year consisting of twelve 30-day months up to, but excluding November 1, 2021, and, the amount of interest payable on any Floating Rate Interest Payment Date during the Floating Rate Period will be computed on the basis of a 360-day year and the number of days actually elapsed. In the event that any scheduled Interest Payment Date for this Note falls on a day that is not a Business Day, then payment of interest payable on such Interest Payment Date will be paid on the next succeeding day which is a Business Day (any payment made on such date will be treated as being made on the date that the payment was first due and no interest on such payment will accrue for the period from and after such scheduled Interest Payment Date); provided, that in the event that any scheduled Floating Rate Interest Payment Date falls on a day that is not a Business Day and the next succeeding Business Day falls in the next succeeding calendar month, such Floating Rate Interest Payment Date will be accelerated to the immediately preceding Business Day, and, in each such case, the amounts payable on such Business Day will include interest accrued to but excluding such Business Day. All percentages used in or resulting from any calculation of Three-month LIBOR shall be rounded, if necessary, to the nearest one hundred-thousandth of a percentage point, with 0.000005% rounded up to 0.00001%.

Any principal and premium, and any such installment of interest, which is overdue shall bear interest at the applicable rate set forth in the previous paragraph (to the extent that the payment of such interest shall be legally enforceable), from the dates such amounts are due until they are paid or made available for payment, and such interest shall be payable on demand. The interest so payable, and punctually paid or duly provided for, on any Interest Payment Date will, as provided in the Indenture, be paid to the Person in whose name this Note is registered at the close of business on the 15th day of the month (whether or not a Business Day) immediately preceding such Interest Payment Date.

Payment of the principal of and interest on this Note will be made at the office or agency of the Company maintained for that purpose, which shall initially be the Corporate Trust Office of the Trustee, in such currency of the United States of America as at the time of payment is legal tender for payment of public and private debts.

Reference is hereby made to the further provisions of this Note set forth on the reverse hereof, which further provisions shall for all purposes have the same effect as if set forth at this place.

Unless the certificate of authentication hereon has been executed by the Trustee referred to on the reverse hereof by manual signature, this Note shall not be entitled to any benefit under the Indenture or be valid or obligatory for any purpose.

[Remainder of this page intentionally left blank. Signature page follows.]

IN WITNESS WHEREOF, the Company has caused this instrument to be duly executed.

Dated:

Attest:

CERTIFICATE OF AUTHENTICATION

This is one of the Securities of the series designated therein referred to in the within-mentioned Indenture.

[Signatures Page to Global Note]

[FORM OF REVERSE OF NOTE]

ENTERPRISE FINANCIAL SERVICES CORP

4.75% Fixed-to-Floating Rate Subordinated Notes due November 1, 2026

This Note is one of a duly authorized issue of Securities of the Company of a series designated as the “4.75% Fixed-to-Floating Rate Subordinated Notes due 2026” (herein called the “Notes”) initially issued in an aggregate principal amount of $50,000,000 on November 1, 2016. Such series of Securities has been established pursuant to, and is one of an indefinite number of series of subordinated debt securities of the Company issued or issuable under and pursuant to the Subordinated Debt Securities Indenture, dated as of November 1, 2016 (the “Base Indenture”), between the Company and U.S. Bank National Association, as Trustee (herein called the “Trustee,” which term includes any successor trustee), as supplemented and amended by the First Supplemental Indenture between the Company and the Trustee, dated as of November 1, 2016 (the “First Supplemental Indenture,” and the Base Indenture as supplemented and amended by the First Supplemental Indenture, the “Indenture”), to which Indenture and any other indentures supplemental thereto reference is hereby made for a statement of the respective rights, limitations of rights, duties and immunities thereunder of the Company, the Trustee and the Persons in whose names Notes are registered from time to time and of the terms upon which the Notes are, and are to be, authenticated and delivered. The terms, conditions and provisions of the Notes are those stated in the Indenture, those made part of the Indenture by reference to the Trust Indenture Act of 1939, as amended (the “Trust Indenture Act”), and those set forth in this Note. To the extent that the terms, conditions and provisions of this Note modify, supplement or are inconsistent with those of the Indenture, then the terms, conditions and other provisions of this Note shall govern to the extent that such terms, conditions and other provisions of this Note are not inconsistent with the terms, conditions and provisions made part of the Indenture by reference to the Trust Indenture Act.

All capitalized terms used in this Note and not defined herein that are defined in the Indenture shall have the meanings assigned to them in the Indenture. To the extent that any capitalized term used in this Note and defined herein is also defined in the Indenture but conflicts with the definition provided in the Indenture, the definition of the capitalized term in this Note shall control.

The indebtedness of the Company evidenced by the Notes, including the principal thereof, premium, if any, Additional Amounts, if any, and interest thereon, is, to the extent and in the manner set forth in the Indenture, subordinate and subject in right of payment to the prior payment in full of all Senior Indebtedness, whether outstanding at the date hereof or hereafter incurred, and on the terms and subject to the terms and conditions set forth in the Indenture, and shall rank pari passu in right of payment with all other Securities and with all other unsecured subordinated indebtedness of the Company and not by its terms subordinate and subject in right of payment to the prior payment in full of debentures, notes, bonds or other evidences of indebtedness of types that include the Notes. Each Holder of this Note, by the acceptance hereof, agrees to and shall be bound by such provisions of the Indenture and authorizes and directs the Trustee on his behalf to take such actions as may be necessary or appropriate to effectuate the subordination so provided.

The Notes are intended to be treated as Tier 2 capital (or its then-equivalent if the Company were subject to such capital requirement) for purposes of capital adequacy guidelines of the Board of Governors of the Federal Reserve System (or any successor regulatory authority with jurisdiction over bank holding companies) (the “Federal Reserve Board”) as then in effect and applicable to the Company. If an Event of Default with respect to Notes shall occur and be continuing, the principal and interest owed on the Notes shall only become due and payable in accordance with the terms and conditions set forth in Article 8 of the Base Indenture and Section 3.02(k) and (o) of the First Supplemental Indenture. Accordingly, the Holder of this Note has no right to accelerate the maturity of this Note in the event that the Company fails to pay interest on any of the Notes, or fails to perform any other obligations under the Notes or in the Indenture that are applicable to the Notes.

The Company may, at its option, redeem the Notes, in whole or in part, at a redemption price equal to 100% of the principal amount of the Notes to be redeemed, plus accrued and unpaid interest (the “Redemption Price”) to but excluding, the date of redemption (the “Redemption Date”), on any Interest Payment Date on or after November 1, 2021. The Company may also, at its option, redeem the Notes before the Stated Maturity Date, in whole or in part, at any time, upon the occurrence of a Tier 2 Capital Event, a Tax Event or a 1940 Act Event. Any such redemption will

be at a redemption price equal to the Redemption Price to, but excluding, the Redemption Date fixed by the Company. No redemption of the Notes by the Company prior to the Stated Maturity Date shall be made without the prior approval of the Federal Reserve Board if such prior approval is or will be required at the scheduled Redemption Date. The provisions of Article 4 of the Base Indenture and Section 3.02(g) of the First Supplemental Indenture shall apply to the redemption of any Notes by the Company.

The Notes are not entitled to the benefit of any sinking fund. The Notes are not convertible into or exchangeable for any other securities or property of the Company or any Subsidiary of the Company.

The Indenture permits, with certain exceptions as therein provided, the amendment thereof and the modification of the rights and obligations of the Company and the rights of the Holders of the Notes at any time by the Company and the Trustee with the consent of the Holders of at least a majority in principal amount of the Outstanding Notes. The Indenture also contains provisions permitting the Holders of specified percentages in principal amount of the Notes at the time Outstanding, on behalf of the Holders of all Notes, to waive certain past defaults under the Indenture and their consequences. Any such consent or waiver by the Holder of this Note shall be conclusive and binding upon such Holder and upon all future Holders of this Note and of any Note issued upon the registration of transfer hereof or in exchange therefor or in lieu hereof, whether or not notation of such consent or waiver is made upon this Note.

As provided in the Indenture and subject to certain limitations therein set forth, the transfer of this Note is registrable in the Register described in Section 305 of the Base Indenture, upon surrender of this Note for registration of transfer at the office or agency of the Company in any place where the principal of and interest on this Note are payable, duly endorsed by, or accompanied by a written instrument of transfer in form satisfactory to the Company and the Registrar duly executed by the Holder hereof or the Holder’s attorney duly authorized in writing, and thereupon one or more new Notes, of authorized denominations and for the same aggregate principal amount, will be issued to the designated transferee or transferees.

The Notes are issuable only in registered form without coupons in minimum denominations of $1,000 and any integral multiples of $1,000 in excess thereof.

The Company and the Trustee and any agent of the Company or the Trustee may treat the Person in whose name this Note is registered as the owner hereof for all purposes, whether or not this Note is overdue, and neither the Company, the Trustee nor any such agent shall be affected by notice to the contrary.

This Security is a global note, represented by one or more permanent global certificates registered in the name of the nominee of The Depository Trust Company (each a “Global Note” and collectively, the “Global Notes”). Accordingly, unless and until it is exchanged for individual certificates, this Note may not be transferred except as a whole by The Depository Trust Company (the “Depositary”) to a nominee of such Depositary or by a nominee of such Depositary or by the Depositary or any nominee to a successor Depositary or any nominee of such successor. Ownership of beneficial interests in this Security will be shown on, and the transfer of that ownership will be effected only through, records maintained by the applicable Depositary or its nominee (with respect to interest of persons that have accounts with the Depositary (“Participants”)) and the records of Participants (with respect to interests of persons other than Participants). Beneficial interests in Notes owned by persons that hold through Participants will be evidenced only by, and transfers of such beneficial interests with such Participants will be effected only through, records maintained by such Participants. Except as provided below, owners of beneficial interests in this Note will not be entitled to have any individual certificates and will not be considered the owners or Holders thereof under the Indenture.

Except in the limited circumstances set forth in the Indenture, Participants and owners of beneficial interests in the Global Notes will not be entitled to receive Notes in the form of individual securities in definitive, non-global form registered in the name or names of persons other than the Depositary or a nominee or nominees thereof and will not be considered Holders of Notes. None of the Company, the Trustee, the Registrar, the Paying Agent or any of their respective agents will be liable for any delay by the Depositary, its nominee or any direct or indirect Participant in identifying the beneficial owners of the related Notes. The Company, the Trustee, the Registrar, the Paying Agent and each of their respective agents may conclusively rely on, and will be protected in relying on, instructions from the Depositary or its nominee for all purposes, including with respect to the registration and delivery, and the respective principal amounts, of the Notes to be issued.

Except as provided in Section 305 of the Indenture, beneficial owners of Global Notes will not be entitled to receive physical delivery of Notes in the form of physical certificates, and no Global Note will be exchangeable except for another Global Note of like denomination and tenor to be registered in the name of the Depositary or its nominee. Accordingly, each person owning a beneficial interest in a Global Note must rely on the procedures of the Depositary and, if such person is not a Participant, on the procedures of the Participant through which such person owns its interest, to exercise any rights of a Holder under the Notes.

The laws of some jurisdictions may require that certain purchasers of securities take physical delivery of those securities in definitive form. Accordingly, the ability to transfer interests in the Notes represented by a Global Note to those persons may be limited. In addition, because the Depositary can act only on behalf of its Participants, who in turn act on behalf of persons who hold interests through Participants, the ability of a person having an interest in Notes represented by a Global Note to pledge or transfer such interest to persons or entities that do not participate in the Depositary’s system, or otherwise to take actions in respect of such interest, may be affected by the lack of a physical definitive security in respect of such interest. None of the Company, the Trustee, the Paying Agent and the Registrar will have any responsibility or liability for any aspect of the records relating to or payments made on account of Notes by the Depositary, or for maintaining, supervising or reviewing any records of the Depositary relating to the Notes.

The Trustee will act as the Company’s Paying Agent with respect to the Notes through its Corporate Trust Office presently located at 50 S 16th St, Suite 2000, Philadelphia, PA 19102. The Company may at any time rescind the designation of a Paying Agent, appoint a successor Paying Agent, or approve a change in the office through which any Paying Agent acts.

Notices to the Holders of registered Notes in the form of Individual Securities will be given to such Holders at their respective addresses in the Register, or in the case of Global Notes, electronic delivery in accordance with DTC’s applicable procedures. The Indenture contains provisions setting forth certain conditions to the institution of proceedings by the Holders of Notes with respect to the Indenture or for any remedy under the Indenture.

THIS NOTE SHALL BE DEEMED TO BE A CONTRACT MADE UNDER THE LAWS OF THE STATE OF NEW YORK.

FORM OF ASSIGNMENT

For value received                  hereby sell(s), assign(s) and transfer(s) unto                  (Please insert social security or other identifying number of assignee) the within Note, and hereby irrevocably constitutes and appoints                  as attorney to transfer the said Note on the books of the Company, with full power of substitution in the premises.