Cardiogenic shock kills roughly half the patients it reaches in the ICU, a mortality burden that has persisted for decades without a single drug specifically approved to treat it. Seismic Pharmaceuticals enrolled the first patient in RESCUE HF-CS, its global Phase 3 trial of istaroxime, on September 9, 2026, setting up the only late-stage program currently designed to change that.
The trial targets approximately 600 patients across sites in the United States, Europe, China, and South America. It follows four completed Phase 2 studies in which more than 350 patients received istaroxime, including a Phase 2b extension study in which cardiac output rose roughly 15% during infusion with no significant increase in heart rate. That last point matters clinically: the inotropes physicians currently use off-label in cardiogenic shock tend to raise myocardial oxygen demand and increase arrhythmia risk, two problems istaroxime’s mechanism is designed to avoid.
Istaroxime works through two simultaneous actions: it inhibits Na/K ATPase, which increases the calcium available for each contraction, and it activates SERCA2a, the pump that clears calcium from the cell between beats. Stimulating SERCA2a accelerates calcium cycling and improves diastolic relaxation, meaning the heart refills more completely before the next beat. Most inotropes address only the squeeze; istaroxime addresses both sides of the cardiac cycle. In the Phase 2b data, the drug also reduced ventricular arrhythmias in patients on continuous 72-hour ECG monitoring, a signal worth watching in Phase 3 where the trial is large enough to power a meaningful event count.
The size of the Phase 3 program relative to the Phase 2 experience (600 patients versus 350 across all prior studies combined) reflects how hard cardiogenic shock trials are to run: patients are critically ill, enrollment windows are narrow, and sites need intensive care infrastructure. An ICU mortality rate of 44.8% in a large prospective analysis confirms how sick this population is and how little time investigators have to capture patients at the right point in their deterioration. The primary enrollment milestone to watch is whether Seismic can sustain site activation across four continents fast enough to keep that 600-patient target within a realistic timeframe.
Jon Napitupulu is Director of Media Relations at The Clinical Trial Vanguard. Jon, a computer data scientist, focuses on the latest clinical trial industry news and trends.
