Effects of betaxolol, a cardioselective β-adrenoceptor antagonist, on cardiohemodynamics and coronary circulation were investigated in two kinds of anesthetized open-chest dog preparations in comparison with those of atenolol and propranolol. When administered intravenously, betaxolol, atenolol and propranolol produced dose-dependent decreases in the heart rate (HR), maximum left ventricular dP/dt ((+)dP/dt), cardiac output (CO) and mean arterial pressure (MAP). Although all three drugs were almost equipotent in decreasing HR, betaxolol was much less potent than atenolol and propranolol in decreasing (+)dP/ dt. Betaxolol decreased the total peripheral resistance (TPR), whereas atenolol and propranolol increased it. In another series of experiments, when administered intravenously, betaxolol, atenolol and propranolol all produced a decrease in the myocardial oxygen consumption (MVO₂) and an increase in the atrioventricular conduction time (AVCT). All three drugs were nearly equipotent in decreasing MVO₂, although betaxolol was less potent than the other two drugs at higher doses (>300 μg/kg). Prolongation of AVCT with propranolol was stronger than those with betaxolol and atenolol. These results suggest that, unlike atenolol and propranolol, the decrease in TPR as well as β₁-adrenoceptor blockade may be responsible for both the hypotensive effect of betaxolol and the decrease in MVO₂ with betaxolol. The result that the cardiodepressant effect of betaxolol was much less potent than those of atenolol and propranolol suggests that betaxolol would be more beneficial than the others in the treatment of ischemic heart desease.