1 The effects of 5 mg/kg acebutolol given intravenously were investigated in anaesthetized dogs after (a) ligation of the left anterior descending coronary artery and (b) coronary reperfusion following 60 min of ligation of the anterior descending coronary artery. 2 Coronary artery ligation produced, after 4 to 6 h, persistent multiple ventricular ectopic beats and abnormalities of R and T waves and of the S-T segment. Administration of acebutolol, after the development of persistent ventricular arrhythmias, restored normal sinus rhythm within 5 min of injection. Electrocardiographic abnormalities were also reduced. 3 Coronary artery reperfusion (following 60 min of ligation) resulted in multiple ventricular ectopic beats, ventricular tachycardia and/or ventricular fibrillation. Pretreatment with acebutolol, 15 min before starting reperfusion, markedly reduced the arrhythmias. 4 Acebutolol did not affect peak inspiratory airway pressure. 5 Acebutolol produced significant bradycardia and slight, transient, hypotension. It was without effect on left ventricular systolic pressure, left ventricular end-diastolic pressure, cardiac output or pulmonary arterial pressure. 6 These results suggest beneficial effects of acebutolol in myocardial ischaemia and coronary reperfusion, without any significant risk of cardiodepression or bronchospasm.