OBJECTIVE To determine if renal dose dopamine (3 microg/kg/min) alters the heart rate (HR) by itself, or if a dopamine infusion alters the HR response to bolus doses of the beta-adrenergic agonist isoproterenol in healthy human subjects. METHODS Prospective study. METHODS Clinical laboratory of a university-affiliated academic medical center. METHODS A total of 15 healthy nonpregnant women and men aged 21 to 44 years. METHODS Subjects were monitored continuously with bedside ECG, pulse oximetry, and ambulatory ECG recording to measure the maximal HR response to separate injections of 10, 20, and 30 ng/kg of isoproterenol, given before, during, and after the infusion of 3 microg/kg/min of dopamine. RESULTS Dopamine in the absence of isoproterenol did not alter baseline HR significantly (62.7+/-2.2 beats/min without dopamine; 65.4+/-2.2 with dopamine; p=0.15). All three doses of isoproterenol increased HR significantly above baseline, both in the presence and absence of dopamine (p<0.001). Dopamine infusion resulted in a higher HR following isoproterenol only for the 20-ng/kg dose. The incremental increases in HR, defined as the difference between peak HR following isoproterenol and baseline HR, were not increased during dopamine infusion for any of the doses of isoproterenol. Nausea was reported by 5 of the 15 subjects during the dopamine infusion. CONCLUSIONS In healthy human subjects, infusion of 3 microg/kg/min of dopamine does not significantly increase the HR when combined with beta-adrenergic stimulation using isoproterenol, suggesting neither an additive nor antagonistic interaction between the two drugs. While our study did not demonstrate an increase in HR in healthy subjects, the risk of increasing the chronotropic response to beta-adrenergic inotropic medications with "renal dose" dopamine in critically ill patients needs to be investigated. The frequency of nausea during dopamine infusion also may influence consideration of using dopamine to augment splanchnic blood flow and renal function in conscious patients.