Background: Propofol has gained widespread popularity but it should at least be questioned in the presence of heart rate lowering medications such as beta-blockers. Esmolol, due to its ultrashort action and cardioselective properties, has been shown to be safe and effective for use in intraoprative tachycardia and hypertension. The purpose of this study is to evaluate the hemodynamic effects of esmolol and propofol under isoflurane anesthesia in dogs. Methods: Six-mongrel dogs were induced with thiopental, intubated and ventilated with a mixture of isoflurane (1 - 1.5 vol%) and oxygen. A pulmonary artery catheter was placed via femoral vein and the femoral artery was cannulated. After stabilization, baseline hemodynamic measurements (HR, MAP, CO, SVR) were obtained. Measurements were repeated 5 and 15 minutes after injection of propofol (2 mg/kg), esmolol (1 mg/kg), and additional esmolol (1 mg/kg) for 30 seconds. Data was analyzed by repeated measurement of ANOVA. P < 0.05 was considered significant. Results: Propofol produced no change in heart rate, MAP, CO and SVR. Heart rate decreased significantly during esmolol admi#nistration and remained decreased up to 15 minutes after the injection whereas the MAP, CO and SVR showed no significant changes. Conclusions: We have demonsttated that the decrease in heart rate continued up to 15 minutes after esmolol administration. These findings suggest that concomittent administration of propofol and esmolol requires monitoring of the heart rate after a bolus intravenous injection of esmolol.