AtriCure (ATRC) 8-K AtriCure Announces Proposed Public Offering of Common Stock

Exhibit 5.1

F. Mark Reuter

D: 513.579.6469
MReuter@KMKLAW.com

May 11, 2020

AtriCure, Inc.

7555 Innovation Way

Mason, Ohio 45040

Re: Registration Statement on FormS-3ASR

Ladies and Gentlemen:

This opinion is furnished to you in connection with the offering by AtriCure, Inc., a Delaware corporation (the “Company”), of up to 4,573,863 shares of the Company’s common stock, par value $0.001 per share (the “Shares”), including up to 596,590 shares that may be sold pursuant to the exercise of an option to purchase additional shares of common stock of the Company, pursuant to a Registration Statement on FormS-3ASR (RegistrationNo. 333-230001) (the “Registration Statement”), filed by the Company on March 1, 2019, with the Securities and Exchange Commission (the “SEC”) under the Securities Act of 1933, as amended (the “Securities Act”), the prospectus included in the Registration Statement (the “Base Prospectus”), and the prospectus supplement related to the Shares filed by the Company with the SEC pursuant to Rule 424(b) promulgated under the Securities Act (together with the Base Prospectus, the “Prospectus”).

We understand that the Shares are to be sold to the underwriters for resale to the public as described in the Prospectus and pursuant to an underwriting agreement dated May 11, 2020 entered into by and between the Company, J.P. Morgan Securities LLC and Piper Sandler & Co., as representatives of the several underwriters (the “Underwriting Agreement”).

We are acting as counsel for the Company in connection with the sale of the Shares by the Company. In such capacity, we have examined the Registration Statement (including exhibits thereto), the Prospectus and the Underwriting Agreement. We have also examined originals or copies, certified or otherwise identified to our satisfaction, of such documents, corporate records, certificates of public officials and other instruments as we have deemed necessary for the purposes of rendering this opinion. In our examination, we have assumed the genuineness of all signatures, the authenticity of all documents submitted to us as originals, the conformity with the originals of all documents submitted to us as copies, the authenticity of the originals of such documents and the legal competence of all signatories to such documents.

May 11, 2020

Page 2

We express no opinion herein as to the laws of any state or jurisdiction other than the General Corporation Law of the State of Delaware (including the statutory provisions and all applicable judicial decisions interpreting those laws) and the federal laws of the United States of America.

On the basis of the foregoing, we are of the opinion that the Shares to be issued and sold by the Company have been duly authorized and, when such Shares are issued and delivered against payment in accordance with the terms of the Underwriting Agreement, such Shares will be validly issued, fully paid and nonassessable.

We consent to the use of this opinion as an exhibit to the Company’s Current Report on Form8-K, to be filed on the date hereof and we consent to the reference of our name under the caption “Legal Matters” in the Prospectus forming part of the Registration Statement.

Very truly yours,

/s/ Keating Muething & Klekamp PLL

KEATING MUETHING & KLEKAMP PLL