8-K

UNITED STATESSECURITIES AND EXCHANGE COMMISSIONWASHINGTON, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934

SeaStar Medical Holding Corporation

(Exact name of Registrant as Specified in Its Charter)

(Former Name or Former Address, if Changed Since Last Report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

☐Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

☐Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

☐Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

☐Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Securities registered pursuant to Section 12(b) of the Act:

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§ 230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§ 240.12b-2 of this chapter).

Emerging growth company ☒

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ☐

Item 8.01 Other Events

As previously disclosed, on August 20, 2024, SeaStar Medical Holding Corporation, (the “Company”), entered into an At the Market Offering Agreement (the “ATM Agreement”) with H.C. Wainwright & Co., LLC (the “Agent”), as sales agent, pursuant to which the Company may offer and sell shares of the Company’s common stock, par value $0.0001 per share (the “Shares”), from time to time in an at-the-market public offering. On July 10, 2025, the Company determined to suspend sales under the ATM Agreement and terminated the continuous offering of the initial aggregate offering price of $25,000,000. As of August 8, 2025, the Company had sold an aggregate of $6.8 million in shares of its common stock under the ATM Agreement.

The Company has determined to resume sales under the ATM Agreement, up to an aggregate offering price of $2,166,305. The Shares sold under the ATM Agreement will be offered and sold pursuant to the Company’s shelf registration statement on Form S-3 (Registration No. 333-275968), which was initially filed with the Securities and Exchange Commission (the “SEC”) on December 8, 2023 and declared effective on December 22, 2023, and a prospectus supplement and the accompanying prospectus relating to the at-the-market offering filed with the SEC on August 8, 2025.

Because there is no minimum offering amount required pursuant to the ATM Agreement, the total number of Shares to be sold under the ATM agreement, if any, and proceeds to the Company, if any, are not determinable at this time. The Company expects to use any net proceeds for general corporate purposes, which may include additions to working capital and capital expenditures.

The Company retains broad discretion over the use of the net proceeds and reserves the right to use these proceeds for different purposes or uses which have not been listed above. Until the Company uses the net proceeds, it intends to invest the funds in investment grade, interest-bearing securities or hold such proceeds in deposit accounts.

A copy of the opinion of the Company’s counsel relating to the validity of the Shares that may be sold pursuant to the ATM Agreement is filed herewith as Exhibit 5.1.

This Current Report on Form 8-K, including the exhibits filed herewith, shall not constitute an offer to sell or the solicitation of an offer to buy the Shares that may be sold pursuant to the ATM Agreement, nor shall there be any offer, solicitation or sale of the Shares in any state or country in which such offer, solicitation or sale would be unlawful prior to registration or qualification under the securities laws of any such state or country.

Item 9.01 Financial Statements and Exhibits

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

EX-5.1

Exhibit 5.1

August 8, 2025

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 Prospectus Supplement (the “Prospectus Supplement”), dated August 8, 2025, to the prospectus, dated December 22, 2023, included in the Registration Statement on Form S-3 (File No. 333-275968) (the “Registration Statement”) filed by the Company with the Commission under the Securities Act of 1933, as amended (the “Securities Act”), relating to the offer and sale by the Company of up to $2,166,305 of shares (the “Shares”) of the Company’s common stock, $0.0001 par value per share (the “Common Stock”), pursuant to that certain at the market offering agreement, dated August 20, 2024 (the “ATM Agreement”), by and among the Company and H.C. Wainwright & Co., LLC (the “Manager”). Capitalized terms used and not otherwise defined herein have the meanings ascribed to them in the ATM 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 ATM 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 a Current Report on Form 8-K to be filed by the Company with the Commission on the date hereof, which Current Report on Form 8-K will be incorporated by reference into the Registration Statement, and to the reference to our firm under the heading “Legal Matters” in the Prospectus Supplement. 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.

DOCPROPERTY "CUS_DocIDChunk0" 4915-0137-7882\2