Inhalation of 40 per cent N2O by nine patients who had occlusive disease in two or more coronary arteries with elevation of left ventricular end-diastolic pressures (LVEDP) significantly decreased arterial pressure (average 5 per cent) and myocardial contractility as measured by dP/dt/CPIP (average 14 per cent), and increased LVEDP (average 21 per cent). N2O had no significant effect in four patients who had angina without angiographically demonstrable coronary arterial disease. It is concluded that N2O depresses myocardial function in patients who have occlusion of the coronary arteries and impaired left ventricular function.