To assess the effects of nitrous oxide on hemodynamics and left ventricular function in man, 30 patients (24 of whom had coronary artery disease) were studied at the time of cardiac catheterization. Left ventricular peak-systolic pressure and end-diastolic volume showed no significant change during nitrous oxide inhalation. The maximum rate of pressure rise declined slightly, but left ventricular end-diastolic pressure and ejection fraction were unchanged. Heart rate and cardiac index declined modestly. The pressure-rate product and left ventricular minute work index decreased, suggesting a decline in myocardial oxygen requirements. These data suggest that nitrous oxide inhalation does not produce important depression of left ventricular performance. The consistent decrease in the determinants of myocardial oxygen demand suggests that use of this analgesic agent may be helpful in patients with coronary heart disease.