Cardiovascular effect of a new compound, K 351, was examined in anesthetized dogs. I.v. injections of .gtoreq. 100 .mu.g/kg of K 351 caused a fall in systemic blood pressure, reduced peripheral vascular resistance, left ventricular enddiastolic pressure, max dP/dt [change in pressure with time] and Vmax, and increased time constant T and PQ interval. Heart rate was reduced with 1 .mu.g/kg K 351. The magnitudes of the changes in heart rate, T and PQ interval were not different between K 351 and propranolol groups, while those in max dP/dt and Vmax caused by K 351 were larger than those induced by the same doses of propranolol. Evidently, K 351 suppressed left ventricular contractility, sinus node activity and atrioventricular conduction through its .beta.-receptor blocking action and reduced peripheral vascular resistance and left ventricular enddiastolic pressure through its vasodilating action.