SeaStar Medical Holding Corp

As filed with the Securities and Exchange Commission on August 8, 2025

Registration No. 333-

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORMS-1

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933

(Exact Name of Registrant as Specified in Its Charter)

3513 Brighton Blvd, Suite 410

Denver, CO 80216

(844) 427-8100

(Address, Including Zip Code, and Telephone Number, Including Area Code, of Registrant’s Principal Executive Offices)

Eric Schlorff

Chief Executive Officer

3513 Brighton Blvd, Suite 410

Denver, CO 80216

(Name, Address, Including Zip Code, and Telephone Number, Including Area Code, of Agent for Service)

Copies to:

Joshua Erekson

Daniel Lyman

Dorsey & Whitney LLP

111 South Main Street, Suite 2100

Salt Lake City, UT 84111

(801) 933-7360

Approximate date of commencement of proposed sale to the public: From time to time after the effective date of this registration statement.

If any of the securities being registered on this Form are to be offered on a delayed or continuous basis pursuant to Rule 415 under the Securities Act of 1933, check the following box. ☒

If this Form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, please check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. ☐

If this Form is a post-effective amendment filed pursuant to Rule 462(c) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. ☐

If this Form is a post-effective amendment filed pursuant to Rule 462(d) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. ☐

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company, or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company” and “emerging growth company” in Rule 12b-2 of the Exchange Act:

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 7(a)(2)(B) of the Securities Act.☐

The registrant hereby amends this Registration Statement on such date or dates as may be necessary to delay its effective date until the registrant shall file a further amendment which specifically states that this Registration Statement shall thereafter become effective in accordance with Section 8(a) of the Securities Act of 1933 or until this Registration Statement shall become effective on such date as the Securities and Exchange Commission, acting pursuant to said Section 8(a), may determine.

The information in this preliminary prospectus is not complete and may be changed. These securities may not be sold until the registration statement filed with the Securities and Exchange Commission is effective. This preliminary prospectus is not an offer to sell nor does it seek an offer to buy these securities in any jurisdiction where the offer or sale is not permitted.

Up to 10,917,218 Shares of Common Stock

Offered by the Selling Securityholders

This prospectus covers the offer and resale from time to time of: (i) up to 5,242,464 shares of common stock, par value $0.0001 per share (“Common Stock” and, as so issuable upon exercise, the “July Common Warrant Shares”) issuable upon exercise of Common Stock purchase warrants (the “July Common Warrants”) with an exercise price of $0.638 per share; (ii) up to 366,972 shares of Common Stock (the “July Placement Agent Shares”) issuable upon exercise of the placement agent Common Stock purchase warrants (the “July Placement Agent Warrants”) with an exercise price of $0.9538 per share; (iii) up to 4,960,544 shares of Common Stock (the “August Common Warrant Shares”) issuable upon exercise of Common Stock purchase warrants (the “August Common Warrants”) with an exercise price of $0.762 per share; and (iv) up to 347,238 shares of Common Stock (the “August Placement Agent Shares”) issuable upon exercise of the placement agent Common Stock purchase warrants (the “August Placement Agent Warrants”) with an exercise price of $1.1088 per share. The July Common Warrants were issued pursuant to that certain Securities Purchase Agreement dated July 10, 2025, in a private placement transaction. The August Common Warrants were issued pursuant to that certain Securities Purchase Agreement dated July 31, 2025, in a private placement transaction. The July Placement Agent Warrants and the August Placement Agent Warrants were issued pursuant to that certain Engagement Agreement dated May 17, 2024, as amended on November 13, 2024 and April 1, 2025. The July Common Warrants, August Common Warrants, July Placement Agent Warrants, and August Placement Agent Warrants are together referred to as the “Warrants”.

We are registering the offer and sale of the Resale Shares on behalf of the Selling Securityholders to satisfy certain registration rights that we have granted to the Selling Securityholders.

Sales of the Resale Shares by the Selling Securityholders may occur at fixed prices, at market prices prevailing at the time of sale, at prices related to prevailing market prices or at negotiated prices. The Selling Securityholders may sell the Resale Shares to or through underwriters, broker-dealers or agents, who may receive compensation in the form of discounts, concessions or commissions from the Selling Securityholders, the purchasers of the Resale Shares, or both.

We are paying the cost of registering the Resale Shares as well as various related expenses. The Selling Securityholders are responsible for all selling commissions, transfer taxes and other costs related to the offer and sale of their Resale Shares. See “Plan of Distribution” for more information about how the Selling Securityholders may sell or dispose of their Resale Shares.

We are a “smaller reporting company” under the federal securities laws and, as such, are subject to reduced public company reporting requirements. See “Implications of Being a Smaller Reporting Company.”

We are an “emerging growth company” under the federal securities laws and, as such, are subject to reduced public company reporting requirements. See “Implications of Being an Emerging Growth Company.”

Our Common Stock and warrants exercisable for one share of Common Stock for $11.50 per share (the “Listed Warrants”) are traded on the Nasdaq Stock Market (“Nasdaq”) under the symbols “ICU” and “ICUCW,” respectively. On August 5, 2025, the closing price of our Common Stock was $0.7484 per share, and the closing price of our Listed Warrants, was $0.0384 per warrant.

Investing in our securities involves a high degree of risk. You should read “Risk Factors” beginning on page 6 of this prospectus, and under similar headings in the documents incorporated by reference in this prospectus, as well as in any amendments or supplements to this prospectus, to read about factors to consider before purchasing our securities.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

The date of this prospectus is , 2025.

TABLE OF CONTENTS

i