The effects of prophylactic infusion of 1 µg · kg−1· min−1nitroglycerin (NTG) on the incidence of ischemia, hypertension, hypotension and perioperative myocardial infarction were studied in 81 patients during coronary artery bypass grafting (CABG). Forty-one patients (Group 1) received NTG and 40 patients (Group 2) received placebo. All patients received fentanyl for anesthesia and pancuronium. Mean arterial pressure (MAP), pulmonary capillary wedge pressure (PCWP), heart rate (HR), and cardiac output (CO) were measured before and after induction of anesthesia, after intubation, before and after chest incision, after sternotomy, after the pericardium was opened, and during normothermic cardiopulmonary bypass. Myocardial ischemia and infarction were diagnosed from the ECG, hypertension was denned as a 20% increase in MAP, and hypotension was defined as a 20% decrease in MAP compared with preinduction values. No significant differences between Groups 1 and 2 in HR, PCWP, or CO were seen. MAP was significantly lower in Group 1 than Group 2 (P< 0.05) before chest incision, but increased to levels equal to Group 2 after sternotomy. Hypertension occurred in 32 Group 2 patients and 25 Group 1 patients (0.05 <P< 0.1). Group 1 patients had 0.95 ± 0.14 episodes per patient of hypertension, while Group 2 patients had 2.10 ± 0.31 episodes (P< 0.05). Hypotension occurred in 20 Group 1 patients but only six Group 2 patients (P< 0.05). There was no difference in the incidence of ischemia. In Group 1, nine patients (22%) had ECG changes of ischemia, while 12 patients in Group 2 (30%) had ischemia. Three patients in each group (7%) had evidence of perioperative myocardial infarction. We conclude that prophylactic administration of 1 µg · kg−1· min−1of NTG during fentanyl anesthesia in patients undergoing CABG did not prevent myocardial ischemia or reduce the incidence of perioperative myocardial infarction, but both lowered the incidence of hypertension, especially during intubation, and increased the incidence of hypotension (P< 0.05).