To determine the maintenance of pharmacodynamic effects of fenoldopam mesylate, a dopamine-1 agonist, the invasive hemodynamic profiles of 33 patients with New York Heart Association functional class III to IV congestive heart failure were examined. Fenoldopam mesylate was initiated at 0.1 micrograms/kg/min and titrated to a cardiac index greater than or equal to 25% above baseline. Upon achievement of optimal hemodynamics, maintenance infusion was begun (mean dose 0.6 micrograms/kg/min). Fenoldopam mesylate (baseline vs maximal effect) decreased systemic vascular resistance by 37% (p less than 0.001), left ventricular filling pressure by 16% (p less than 0.05) and mean arterial pressure by 11% (p less than 0.05), with an associated augmentation in cardiac index and stroke volume index by 27% (p less than 0.001). Attenuation of hemodynamic effect (maximal effect vs time) was noted in cardiac index (14% p less than 0.001), systemic vascular resistance (13% p less than 0.05) and stroke volume index (13% p less than 0.05). None of the parameters exhibited complete attenuation to baseline values. Fenoldopam mesylate improves cardiac output and lowers systemic vascular resistance with relative attenuation of pharmacodynamic effect during a 24-hour intravenous infusion.