New Data from the Phase II ARCHER Trial Demonstrate CardiolRx(TM) Improves Heart Structure in Patients with Acute Myocarditis, Supporting Expansion Across Inflammatory Cardiac Conditions

• Phase II ARCHER trial showed a significant reduction in left ventricular (LV) mass (p=0.0117) and improvements in multiple key cardiac MRI (CMR) measures of structural heart recovery in patients with acute myocarditis.

• Results provide clinical evidence that CardiolRx™ reduces inflammation-driven structural damage in the heart, an important cause of heart failure progression.

The ARCHER data strengthen the scientific and clinical rationale for Cardiol's lead Phase III program in recurrent pericarditis (MAVERIC) and support broader development across inflammatory cardiac conditions.

Chronic inflammation is a central driver of adverse cardiac remodeling and heart failure, yet there are currently no approved therapies that directly target this underlying biology.

Cardiol Therapeutics to host webcast and conference call to discuss positive ARCHER results and next steps for CardiolRx™ today at 8:30 a.m. EST.

Toronto, Ontario--(Newsfile Corp. - December 1, 2025) - Cardiol Therapeutics Inc. (NASDAQ: CRDL) (TSX: CRDL) ("Cardiol" or the "Company"), a clinical-stage life sciences company advancing anti-inflammatory and anti-fibrotic therapies for heart disease, today announced new and comprehensive data from ARCHER, a randomized double-blind, placebo-controlled, multi-center Phase II clinical trial of CardiolRx™ in patients with acute myocarditis. The data show meaningful improvements in cardiac MRI (CMR) measures of myocardial recovery in patients with acute myocarditis, a potentially fatal condition caused by viral infections, autoimmune diseases, immune checkpoint inhibitor therapy to treat cancers, and exposure to cardiotoxic substances.

"The ARCHER results show that CardiolRx™ can drive meaningful structural recovery in the hearts of patients with acute myocarditis," said Dr. Andrew Hamer, Chief Medical Officer and Head of Research & Development of Cardiol Therapeutics. "We are seeing in these patients the same beneficial cardiac changes we previously observed in multiple pre-clinical heart failure models, strengthening our confidence in CardiolRx™ as a potential therapy across multiple inflammatory cardiac conditions."

Key findings from the ARCHER trial presented this past weekend included a marked 9.2-gram reduction in left ventricular (LV) mass (p=0.0117), along with reductions in two parameters that directly impact the heart's LV mass: extracellular volume (ECV), a measure that reflects inflammation and fibrosis outside the heart muscle cells and intercellular volume (ICV), a measure of swelling and enlargement of the heart cells. Together, these results indicate a meaningful structural improvement in the heart that is consistent with recovery from inflammation-driven edema.