(S)-Alprenolol is a more active stereoisomer of antihypertensive beta-blocker alprenolol. Its activity against beta-adrenoreceptor is 100 times greater than the activity of (R)-alprenolol. In a model of ventricular arrhythmias produced by ligation of the left coronary artery, (S)-alprenolol was effective at 7.5 mg/kg, whereas (R)-alprenolol abolished the ventricular arrhythmia by cumulative dose of 15.5 mg/kg. As a most active enantiomer of alprenolol, the compound was used as a tool to study beta-adrenergic receptors.