In dogs i.v. bepridil (2.5 mg/kg) increased coronary sinus blood flow PVO2. Arterial pressure was briefly lowered, and heart rate was slowed in animals with intact or denervated hearts, or after propranolol administration. Ventricular inotropism was reduced at higher doses. Bepridil (5 mg/kg i.v.) showed a partial antagonist activity on isoprenaline cardiovascular effects (or cardiac sympathetic stimulation effects), i.e., tachycardia, increase in left dP/dt max [maximal change in pressure with time] and diastolic hypotension. The antitachycardia activity was particularly pronounced. It was non-competitive and non-specific, since glucagon, theophylline- and papaverine-induced tachycardia were also reduced. The continuous infusion of high doses of bepridil did not cause any disturbance in atrioventricular or intraventricular conduction. In rats, after 50 mg/kg per day orally, bepridil did not alter myocardial noradrenaline [norepinephrine] levels.