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A double-blind, randomized study was conducted in 82 patients having coronary revascularization procedures and who were given either butorphanol tartrate (N = 42) or morphine sulfate (N = 40) as analgesics. Anesthesia was induced by combining diazepam with sufficient amounts of the two study drugs to achieve loss of consciousness. Anesthesia was maintained with a mixture of N2O-O2 (50%) and, as needed, increments of either 1.0 mg of butorphanol (BT) or 5 mg of morphine (MS) intravenously. Halothane or enflurane were added if it was felt to be necessary. Hemodynamic and blood gas measurements were made after premedication, after induction, after the skin incision, and after entry into the intensive care unit. The average amount of BT required was about one-fifth the amount of MS given; the average amounts of diazepam and pancuronium were similar in both groups. There was a slight increase in heart rate after induction in both groups, with a slight decrease of systolic arterial pressure after incision in patients given MS. There were no other significant changes in systolic pressure or in either diastolic blood pressures or rate pressure product. Systemic vascular resistance index decreased and cardiac index increased immediately after induction in patients given MS, followed by a subsequent decrease in cardiac index after incision in both groups. Significant increases of pulmonary vascular resistance index were noted after incision and in the postoperative period in the two groups. Anesthesia was supplemented with an inhalation anesthetic after surgery was started in 87% of patients given MS and 73% of those receiving BT. MS and BT were found to be equally satisfactory for balanced anesthesia during coronary bypass surgery; though hemodynamic changes were more common with BT, they were minimal and of no statistical or clinical significance.