Myocardial ischemia before and during coronary artery surgery is significant, because patients who develop perioperative myocardial ischemia have an increased incidence of postoperative myocardial infarctions. Thus, the prevention of ischemic episodes is of great importance. This study was undertaken to (1) compare the effects of intravenous nitroglycerin (NTG) with isosorbide dinitrate (ISDN); (2) investigate if the continuous infusion of nitrates had beneficial effects on cardiac performance and metabolism; and (3) compare the control of blood pressure with the nitrates versus halothane during a standardized anesthetic. Twenty-one patients participated in the study, and all had the following: a radial arterial catheter, peripheral venous catheter, 7F pulmonary artery catheter, and Baim coronary sinus flow catheter. The study was carried out in the prebypass period beginning with awake measurements of baseline parameters, and ending after median sternotomy. The patients were divided into three groups: group 1 received an infusion of NTG; group 2 received an infusion of ISDN; and group 3, the control, received neither nitrate, but halothane was added to control hemodynamics. Measurements were made at the following time intervals: (1) baseline; (2) after 5 minutes of the nitrate infusions while awake (groups 1 and 2); (3) after induction of anesthesia, laryngoscopy, and intubation; and (4) after median sternotomy. In groups 1 and 2, the nitrates were infused at 0.1 mg/kg/h for 5 minutes. Thereafter, blood pressure control and treatment of episodic hypertension were achieved by alteration of the rate of nitrate infusions, or, in group 3, by 0.5% to 2% of inspired halothane.(ABSTRACT TRUNCATED AT 250 WORDS)