Left ventricular function was examined by echocardiography and systolic time intervals in nine healthy male volunteers, who ingested ethanol 0.35 g/kg 4 hr after a 50-mg peroral dose of calcium cyanamide, an aldehyde dehydrogenase inhibitor. Accumulation of acetaldehyde in blood was accompanied by marked increases in heart rate (53%) and cardiac output (78%) as well as by decreases in diastolic arterial blood pressure (19%) and peripheral vascular resistance (46%). Ejection fraction and maximum circumferential fibre shortening velocity increased by 25 and 47%, respectively; the preejection period/ejection time ratio decreased by 31%. 4-Methylpyrazole, an alcohol dehydrogenase inhibitor, efficiently reduced blood acetaldehyde levels when injected intravenously (7 mg/kg) at the height of the reaction. It was as effective as intravenous propranolol (0.1 mg/kg) in attenuating the hyperdynamic circulation and stabilized arterial blood pressure better than propranolol. We conclude that even a very mild alcohol intoxication (30-50 mg/100 ml) causes a marked enhancement of cardiac function, in addition to vasodilation, in subjects with impaired acetaldehyde oxidation. These changes are reversed by preventing acetaldehyde formation through alcohol dehydrogenase inhibition.