BACKGROUND: The purpose of this study was to compare the time course of the bradycardia and hypotensive effects of esmolol. METHODS: Thirty patients who undergoing gynecologic operation were anesthetized with nitrous oxide and enflurane. After the steady state of anesthesia was achieved, esmolol 500microgram/kg for 1 minute followed by 25, 50, or 100microgram/kg/min for 60minuts infused by intravenous catheter. Heart rate, mean arterial pressure, cardiac index, stroke volume, and systemic vascular resistance was measured by 1, 3, 5, 10, 15, 20, 25, 30, 45, and 60 minutes. RESULTS: Heart rate was changed abruptly within 3 to 5 minutes, and decreased rapidly for 15minutes. Mean arteral pressure was decreased rapidly for 30 minutes, but slower than heart rate. Cardiac index was decreased rapidly for 20 minutes and differed significantly on the dose of 25, 50, 100microgram/kg. Stroke volume was decreased for 30 minutes, and systemic vascular resistance was increased rapidly for 10 minutes. It was decided the onset time that was expressed 90% of ultimate response of esmolol effect, and was calculated in each group. The onset time of heart rate of esmolol 25, 50, 100microgram/kg were 8.0 +/- 4.1, 4.8 +/- 2.3, 8.1 +/- 4.4 minutes, the time of mean arterial pressure were 30.0 +/- 7.5, 21.1 +/- 6.2, 19.9 +/- 7.8 minutes, and the time of cardiac index were 25.1 +/- 4.7, 14.8 +/- 5.0, 14.2 +/- 4.6 minutes. Thus heart rate, mean arterial pressure, cardiac index, stroke volume, and systemic vascular resistance responses of administration of esmolol did not occur with equal rapidity. CONCLUSIONS: Thus although esmolol has an ultrashort kinetic half life, only the heart rate effect can be considered to have an ultrashort onset.