The haemodynamic effects of a continuous intravenous infusion of salbutamol (15 to 30 microgram/min) and nitroprusside (50 to 100 microgram/min) were compared in 9 patients after cardiac surgical operations. The mean falls in left atrial pressure and systemic vascular resistance were similar with the two drugs but salbutamol caused a greater increase in heart rate, maximum acceleration of aortic blood flow, and maximum rate of change of left ventricular power. Because these differences would cause greater myocardial oxygen consumption with salbutamol and because the infusion of salbutamol is less easily controlled, nitroprusside is the preferred drug after cardiac operations.