The hemodynamic, coronary sinus blood flow and myocardial metabolic effects of 0.15 mg/kg body weight of intravenously administered propranolol were studied in 19 patients with coronary artery disease and 6 normal patients. Atrial pacing was performed in all patients and produced angina in 15 of the 19 patients with coronary artery disease. In these patients propranolol reduced heart rate from 78 to 69 beats/min, cardiac index from 3.0 to 2.6 liters/min per m2 and left ventricular stroke work index from 47 to 43 g-m/m2; it increased total peripheral resistance from 24 to 28 units and lactate extraction from 16.3 to 22.5%. There was no significant change in mean arterial pressure, left ventricular end-diastolic pressure, coronary sinus blood flow or myocardial oxygen consumption. During a second pacing stress propranolol produced clinical improvement in 9 of the 15 patients who experienced angina initially. The improvement was associated with less severe abnormalities in S-T depression and left ventricular end-diastolic pressure, increased lactate extraction and no significant change in coronary sinus blood flow or myocardial oxygen consumption. Thus, propranolol appears to be capable of modifying the anginal threshold as determined with atrial pacing, and the clinical response appears to be independent of global changes in coronary sinus blood flow and myocardial oxygen consumption.