This study was designed to evaluate the possibility of esmolol to attenuate the cardiovascular reflex due to the induction of general anesthesia, tracheal intubation and/or surgical stimulations during open heart surgery. Esmolol was infused continuously to each patient by 150 ug/kg/min from 2 minutes prior to the completion of the induction of anesthesia and then by 75 ug/kg/min throughout the skin-incision. In patients undergoing coronary bypass grafts, esmolol group of 5 individuals did not show any significant change in hemodynamics in contrast to the control group of 5 individuals, which showed singificant decreases in systolic and mean arterial pressure(p<0.05). The plasma concentrations of the catecholamines in the esmolol group were not significantly different from those in control. In patients undergoing valve replacement, esmolol group did not show any significant difference in hemodynamics from control. The plasma concentrations of the catecholamines in the esmolol group were not changed by the anesthetic and surgical procedures in contrast to the control group, which showed 3 times increase (p<0.05) in norepinephrine level and 8 times increase (p<0.05) in epinephrine level. The results of these experiments demonstrate that esmolol can suppress the hemodynamic refiex and catecholamine-release due to the stimulations of anesthetic and surgical procedures under the general anesthesia by a high concentration of fentanyl, and that esmolol can be administered safely to attenuate the hazardous sympathetic reflexes.