(Mark One)☒QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF1934 For the quarterly period endedMarch 31, 2026 OR ☐TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF1934 FOR THE TRANSITION PERIOD FROM TO Commission File Number 001-39927 SEASTAR MEDICAL HOLDING CORPORATION (Exact name of Registrant as specified in its Charter) Delaware(State or other jurisdiction ofincorporation or organization)3513 Brighton Blvd., Suite 410Denver, CO(Address of principal executive offices) Registrant’s telephone number, including area code: (844) 427-8100 Securities registered pursuant to Section 12(b) of the Act: Indicate by check mark whether the Registrant: (1) has filed all reports required to be filed by Section 13 or 15(d) of the SecuritiesExchange Act of 1934 during the preceding 12 months (or for such shorter period that the Registrant was required to file suchreports), and (2) has been subject to such filing requirements for the past 90 days. Yes☐No☒ Indicate by check mark whether the Registrant has submitted electronically every Interactive Data File required to be submittedpursuant to Rule 405 of Regulation S-T (§232.405 of this chapter) during the preceding 12 months (or for such shorter period thatthe Registrant was required to submit such files). Yes☒No☐ Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, smallerreporting company, or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smallerreporting company,” and “emerging growth company” in Rule 12b-2 of the Exchange Act. Large accelerated filer☐Non-accelerated filer☒Emerging growth company☒ Accelerated filer☐Smaller reporting company☒ If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period forcomplying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act.☐ Indicate by check mark whether the Registrant is a shell company (as defined in Rule 12b-2 of the Exchange Act ). Yes☐No☒ Indicate by check mark whether the registrant has filed all documents and reports required to be filed by Sections 12, 13 or 15(d) ofthe Securities Exchange Act of 1934 subsequent to the distribution of securities under a plan confirmed by a court. Yes☐No☒ As of May 7, 2026, the registrant had 3,997,002shares of common stock, $0.0001 par value per share, outstanding. SeaStar Medical Holding CorporationMarch 31, 2026Table of Contents PART I.FINANCIAL INFORMATION Item 1.Condensed Consolidated Financial Statements (Unaudited)Condensed Consolidated Balance Sheets (March 31, 2026Unaudited)Condensed Consolidated Statements of Operations (Unaudited)Condensed Consolidated Statements of Changes in Stockholders’Equity/(Deficit) (Unaudited)Condensed Consolidated Statements of Cash Flows (Unaudited)Notes to Condensed Consolidated Financial Statements (Unaudited)Item 2.Management’s Discussion and Analysis of Financial Condition and Results of OperationsItem 3.Quantitative and Qualitative Disclosures About Market RiskItem 4.Controls and Procedures PART II.OTHER INFORMATION Item 1.Legal ProceedingsItem 1A.Risk FactorsItem 2.Unregistered Sales of Equity Securities and Use of ProceedsItem 3.Defaults Upon Senior SecuritiesItem 4.Mine Safety DisclosuresItem 5.Other InformationItem 6.ExhibitsSignatures PART I—FINANCIAL INFORMATION SeaStar Medical Holding CorporationCondensed Consolidated Balance Sheets(in thousands, except for share and per-share amounts) SeaStar Medical Holding CorporationCondensed Consolidated Statements of Operations(unaudited)(in thousands, except for share and per-share amounts) Three Months Ended March 31,20262025Net revenue$495$293Cost of goods sold46—Gross profit449293Operating expensesResearch and development2,3442,431General and administrative1,7081,684Total operating expenses4,0524,115Loss from operations(3,603)(3,822)Other income (expense)Interest income9148Interest expense(6)(11)Change in fair value of warrants liability—16Total other income, net8553Loss before provision for income taxes(3,518)(3,769)Provision for income taxes33Net loss$(3,521)$(3,772)Net loss per share of common stock, basic and diluted$(0.90)$(4.38)Weighted-average common shares outstanding, basic and diluted3,918,339861,794 SeaStar Medical Holding CorporationCondensed Consolidated Statements of Changes in Stockholders’Equity/(Deficit)(unaudited)(in thousands, except for share and per-share amounts) SeaStar Medical Holding CorporationCondensed Consolidated Statements of Cash Flows(unaudited)(in thousands) SeaStar Medical Holding CorporationNotes to the Condensed Consolidated Financial Statements (Unaudited)March 31, 2026 Note 1. Description of Business Organization and Description of Business SeaStar Medical Holding Corporation, a Delaware corporation (“SeaStar”) and i




