A β-adrenergic receptor antagonist; antagonizes tachycardia induced by the β-AR agonist isoproterenol in dogs and anesthetized cats; cardioselective, antagonizing tachycardia, diastolic hypotension, and bronchodilation (ED50s = 0.09, 0.9, and 10.2 mg/kg, respectively); restores normal sinus rhythm in an ouabain-induced canine model of cardiac arrhythmia,