Omecamtiv mecarbil is a selective cardiac myosin activator. In the phase II, pharmacokinetic COSMIC-HF study, this drug was associated with decreased ventricular diameters and improvements in cardiac function. A total of 148 patients with chronic heart failure and left ventricular ejection fraction ≤40% were randomly assigned to fixed-dose omecamtiv mecarbil (25 mg twice daily), omecamtiv mecarbil at a dose guided by pharmacokinetics (25 mg twice daily titrated to 50 mg), or placebo. After 20 weeks, the pharmacokinetic-guided group had increases in systolic ejection time (+25 ms) and stroke volume (+3.6 ml), and reductions in left ventricular end-systolic diameter (–1.8 mm), left ventricular end-diastolic diameter (–1.3 mm), heart rate (–3 bmp), and plasma N-terminal pro-B-type natriuretic peptide level (–970 pg/ml), compared with placebo. “Our findings support the hypothesis that directly and specifically improving cardiac function with a cardiac myosin activator results in favourable ventricular remodelling,” conclude the investigators.