Exhibit 4.12

EXECUTION VERSION

Supplemental Indenture Joining Successor Company

December 1, 2016

EIGHTH SUPPLEMENTAL INDENTURE, dated as of December 1, 2016 (this “Supplemental Indenture”), among Envision Healthcare Holdings, Inc., a Delaware corporation (together with its successors and assigns, the “Company”), each of the existing Subsidiary Guarantors under the Indenture (as defined below) party hereto (each an “Existing Guarantor”) and Wilmington Trust, National Association, as Trustee under the Indenture referred to below.

W I T N E S S E T H:

WHEREAS, Envision Healthcare Intermediate Corporation (the “Existing Issuer”), the Existing Guarantors and the Trustee have heretofore become parties to an Indenture, dated as of June 18, 2014 (as amended, supplemented, waived or otherwise modified, the “Indenture”), providing for the issuance of Notes in series;

WHEREAS, pursuant to that certain Agreement and Plan of Merger among the Company, AmSurg Corp., a Tennessee corporation, and New Amethyst Corp., a Delaware corporation and a wholly owned subsidiary of AmSurg Corp., the Existing Issuer merged with and into the Company, with the Company as the surviving entity continuing its existence as a corporation under the laws of the State of Delaware;

WHEREAS, Section 502 of the Indenture provides that upon any transaction involving the Existing Issuer in accordance with Section 501 in which the Existing Issuer is not the Successor Company (as defined in the Indenture), the Successor Company shall succeed to, and be substituted for, and may exercise every right and power of, the Existing Issuer under the Indenture, and thereafter the Existing Issuer shall be relieved of all obligations and covenants under the Indenture; and

WHEREAS, pursuant to Section 901(2) of the Indenture, the parties hereto are authorized to execute and deliver this Supplemental Indenture to amend the Indenture, without the consent of any Holder.

NOW, THEREFORE, in consideration of the foregoing and for other good and valuable consideration, the receipt of which is hereby acknowledged, the Company, the Existing Guarantors and the Trustee mutually covenant and agree for the benefit of the Holders of the Notes as follows:

1. Defined Terms. As used in this Supplemental Indenture, terms defined in the Indenture or in the preamble or recital hereto are used herein as therein defined. The words “herein,” “hereof” and “hereby” and other words of similar import used in this Supplemental Indenture refer to this Supplemental Indenture as a whole and not to any particular section hereof.

2. Assumption of Obligations. The Company hereby expressly assumes all of the obligations of the Existing Issuer under the Notes and the Indenture and agrees to pay, perform and discharge when due each and every debt, obligation covenant and agreement incurred, made or to be paid, performed or discharged by the Existing Issuer under the Indenture and the Notes. The Company hereby agrees to be bound by all the terms, provisions and conditions of the Indenture and the Notes and agrees that it shall be the Successor Company and shall succeed to, and be substituted for, and may exercise every right and power of, the Existing Issuer under the Indenture and the Notes.

3. Agreement to Guarantee. Each Existing Guarantor hereby agrees, jointly and severally with the other Existing Guarantors and fully and unconditionally, to guarantee the Subsidiary Guaranteed Obligations under the Indenture and the Notes on the terms and subject to the conditions set forth in Article XIII of the Indenture and to be bound by (and shall be entitled to the benefits of) all other applicable provisions of the Indenture as a Subsidiary Guarantor.

4. Termination, Release and Discharge. Each Existing Guarantor’s Subsidiary Guarantee shall terminate and be of no further force or effect, and each Existing Guarantor shall be released and discharged from all obligations in respect of such Subsidiary Guarantee, as and when provided in Section 1303 of the Indenture.

5. Parties. Nothing in this Supplemental Indenture is intended or shall be construed to give any Person, other than the Holders and the Trustee, any legal or equitable right, remedy or claim under or in respect of each Existing Guarantor’s Subsidiary Guarantee or any provision contained herein or in Article XIII of the Indenture.

6. Governing Law. THIS SUPPLEMENTAL INDENTURE SHALL BE GOVERNED BY AND CONSTRUED IN ACCORDANCE WITH THE LAWS OF THE STATE OF NEW YORK. THE TRUSTEE, THE COMPANY, ANY OTHER OBLIGOR IN RESPECT OF THE NOTES AND (BY THEIR ACCEPTANCE OF THE NOTES) THE HOLDERS AGREE TO SUBMIT TO THE JURISDICTION OF ANY UNITED STATES FEDERAL OR STATE COURT LOCATED IN THE BOROUGH OF MANHATTAN, IN THE CITY OF NEW YORK IN ANY ACTION OR PROCEEDING ARISING OUT OF OR RELATING TO THIS SUPPLEMENTAL INDENTURE.

7. Ratification of Indenture; Supplemental Indentures Part of Indenture. Except as expressly amended hereby, the Indenture is in all respects ratified and confirmed and all the terms, conditions and provisions thereof shall remain in full force and effect. This Supplemental Indenture shall form a part of the Indenture for all purposes, and every Holder of Notes heretofore or hereafter authenticated and delivered shall be bound hereby. The Trustee makes no representation or warranty as to the validity or sufficiency of this Supplemental Indenture or as to the accuracy of the recitals to this Supplemental Indenture.

8. Counterparts. The parties hereto may sign one or more copies of this Supplemental Indenture in counterparts, all of which together shall constitute one and the same agreement.

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9. Headings. The section headings herein are for convenience of reference only and shall not be deemed to alter or affect the meaning or interpretation of any provisions hereof.

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IN WITNESS WHEREOF, the parties hereto have caused this Supplemental Indenture to be duly executed as of the date first above written.

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