Seastar Medical Holding Corp — S-1 exhibit

Exhibit 5.1

April 28, 2026

SeaStar Medical Holding Corporation

3513 Brighton Blvd, Suite 410

Denver, Colorado 80216

We have acted as counsel to SeaStar Medical Holding Corporation, a Delaware corporation (the “Company”), in connection with the filing by the Company with the Securities and Exchange Commission (the “Commission”) of a Registration Statement on Form S-1 filed by the Company with the Commission under the Securities Act of 1933, as amended (the “Securities Act”), relating to the resale of up to 1,664,543 shares (the “Shares”) of common stock, par value $0.0001 per share (the “Common Stock”), of the Company (the “Shares) by the selling stockholder (the “Selling Stockholder”) identified in the Registration Statement. The Company may issue and sell the Shares to the Selling Stockholder from time to time, in each case, pursuant to the purchase agreement, dated April 25, 2025, by and between the Company and the Selling Stockholder (the “Purchase Agreement”)

We have examined such documents and have reviewed such questions of law as we have considered necessary or appropriate for the purposes of our opinions set forth below. In rendering our opinions set forth below, we have assumed the authenticity of all documents submitted to us as originals, the genuineness of all signatures and the conformity to authentic originals of all documents submitted to us as copies. We have also assumed the legal capacity for all purposes relevant hereto of all natural persons. As to questions of fact material to our opinions, we have relied upon certificates or comparable documents of officers and other representatives of the Company and of public officials.

Based on the foregoing, we are of the opinion that the Shares, when issued and delivered against payment of the consideration therefor specified in the Purchase Agreement, will be validly issued, fully paid and non-assessable.

Our opinions expressed above are limited to the Delaware General Corporation Law.

We hereby consent to the filing of this opinion as an exhibit to the Registration Statement, and to the reference to our firm under the heading “Legal Matters” in the prospectus constituting part of the Registration Statement. In giving this consent, we do not admit that we are within the category of persons whose consent is required under Section 7 of the Securities Act or the rules and regulations of the Commission thereunder.

JBE/DPL