Although amrinone has favorable hemodynamic effects in patients with congestive heart failure, little is known about its effects on coronary blood flow (CBF). We compared the effects of intravenous low-dose dobutamine and amrinone on CBF in 10 patients with dilated cardiomyopathy using a Doppler guidewire. We infused dobutamine at a dose of 5 and 10 mg/kg/min for 5 min. After the end of each stage, coronary flow velocity (CFV) and coronary arterial diameter (CAD) in the proximal left anterior descending coronary artery, and hemodynamic variables were obtained. After the CFV and hemodynamics returned to baseline, we infused 1 mg/kg of amrinone over 5 min, and obtained these variables at 5 and 10 min after the cessation of the infusion. CAD did not increase with dobutamine, but significantly increased after amrinone (% increase: 10 6 7%; P F 0.001 vs. baseline). CFV progressively increased with dobutamine (5 mg/kg/min: 21 6 26%; P F 0.05 vs. baseline; 10 mg/kg/min: 53 6 42%; P F 0.005 vs. baseline and 5 mg/kg/min), but slightly decreased after amrinone (24 6 17%; P 5 not significant vs. baseline). CBF increased during dobutamine (5 mg/kg/min: 25 6 29%; P F 0.05; 10 mg/kg/min: 66 6 55%; P F 0.005) and after amrinone (19 6 22%; P F 0.05) compared to that at baseline. Although there was a significant correlation between the percent increase in CFV and that in dP/dt during dobutamine infusion (r 5 0.82, P F 0.001), this correlation was not observed after amrinone (r 5 0.23). In conclusion, although both agents significantly increased CBF in patients with dilated cardiomyopathy, they do so by different mechanisms. Amrinone mainly increases CBF by causing dilatation of epicardial coronary arteries. These results suggest that amrinone has beneficial effects on coronary flow dynamics in dilated cardiomyopathy.