The effects of nitroprusside and nifedipine on myocardial oxygen consumption (MVO2), catecholamine release, and left ventricular (LV) function (using 2D transesophageal echocardiography) were compared. Thirty-seven patients undergoing coronary artery surgery, anesthetized with fentanyl, 100 micrograms/kg, were studied. All had good LV function and had been receiving long-term oral beta-blocking therapy. Patients were randomly allocated to one of three groups. Group C (n = 12) received no vasodilator and served as control. Group S (n = 13) received nitroprusside at an initial rate of 1 microgram/kg/min. Group N (n = 12) received nifedipine at an initial rate of 0.7 microgram/kg/min. Baseline measurements were obtained ten minutes after intubation. Vasodilator therapy was then started in groups S and N. Infusion rates were adjusted to maintain systolic blood pressure (SBP) between 80% and 120% of baseline values. Additional measurements were made ten minutes after the start of the infusion, ie, before surgery (in group C immediately before surgery), and after sternotomy when the pericardium was opened. The mean (+/- SD) total dose requirements were 1.9 +/- 0.5 micrograms/kg/min for nitroprusside and 1.1 +/- 0.2 micrograms/kg/min for nifedipine. The mean (+/- SD) total infusion time was 31 +/- 5 minutes for nitroprusside and 32 +/- 11 minutes for nifedipine. After sternotomy, heart rate increased in all groups. At this time arterial blood pressure and systemic vascular resistance (SVR) increased in group C. SVR was decreased after the first ten minutes of nitroprusside infusion and after sternotomy in group S. Coronary sinus blood flow, MVO2, and myocardial norepinephrine release increased in group N, but not in groups C or S. After sternotomy, LV percentage area reduction increased in groups S and N, but not in group C. In group N there was a significant correlation (r = 0.65; P less than .05) between the increases in MVO2 and LV percentage area reduction, an estimate of myocardial function. Lactate production occurred in two patients in group C after sternotomy. This was not associated with ECG changes, but in one patient regional wall motion abnormalities developed. No evidence of myocardial ischemia was observed in groups S and N. However, in contrast to nitroprusside, the use of nifedipine was associated with increases in MVO2, myocardial norepinephrine release, and inotropy.