Reports evaluating amrinone's effects in normal (intact) human subjects are complex and difficult to interpret because of the drug's diverse effects on myocardial function, resistance vessels, and vascular capacitance. In this study, 1.5 mg/kg of amrinone was administered as an intravenous bolus to cardiac surgical patients during constant flow cardiopulmonary bypass to determine its isolated effects on venous capacitance and vascular resistance. We noted a significant decrease in vascular resistance up to 8 min after injection and a 460 +/- 160 ml (mean +/- SD) decrease in venous reservoir volume 10 min after injection. Amrinone has potent venous and arterial vasodilating properties that make it a unique drug for treating congestive heart failure in addition to its reported positive inotropic effects.