Bepridil, a new anti-anginal drug, increases coronary blood flow and reduces myocardial oxygen consumption. The comparative effects of bepridil (2.5 mg.kg-1), nitroglycerin (40 microgram/.kg-1) and propranolol (0.5 mg.kg-1) on myocardial performance, were studied in anesthetized dogs. All drugs were injected intravenously within 60 sec. Continuous recordings of left ventricular end-diastolic pressure, peripheral arterial pressure and external ventricular dimensions were made during a 31 min period following drug administration. Similarly, several contractility indices were calculated during the phase of isovolumic contraction. Bepridil was found to decrease left ventricular work, by 14.3 +/- 4.4% while increasing aortic blood flow by 24 +/- 6%. In addition, this compound weakly and only briefly decreased contractility, but reduced the afterload more markedly by 34.2 +/- 3.8%. The external ventricular circumference was only slightly increased. Nitroglycerin reduced aortic flow, ventricular dimensions together with the pre- and afterloads. Propranolol reduced aortic flow while considerably increasing ventricular dimensions and preload. Thus, in the anesthetized dog, the intravenous administration of bepridil decreases left ventricular work while increasing aortic blood flow. Both effects occur during mild and prolonged bradycardia.