BACKGROUND: A "renal dose" of dopamine is often used to increase renal blood flow; however, data on the magnitude of effect and site of action in patients with heart failure are scarce. METHODS AND RESULTS: Renal effects of intravenous dopamine (1, 2, 3, 5, and 10 mug . kg(-1) . min(-1)) were evaluated in 13 patients with chronic heart failure. Renal blood flow was calculated from renal artery cross-sectional area measured with intravascular ultrasound and renal blood flow velocity-time integral measured by the intravascular Doppler technique. Cross-sectional area increased and was significantly higher than baseline (0.30+/-0.04 cm(2)) at 5 mug . kg(-1) . min(-1) (0.36+/-0.05 cm(2)) and 10 mug . kg(-1) . min(-1) (0.38+/-0.06 cm(2)). The velocity-time integral was significantly higher than baseline (22+/-3 cm) at doses of 3 and 5 mug . kg(-1) . min(-1) (both 31+/-4 cm). Renal blood flow increased, whereas renal vascular resistance decreased, reaching statistical significance at 2 mug . kg(-1) . min(-1) through 10 mug . kg(-1) . min(-1). Cardiac output gradually increased, reaching statistical significance at doses of 5 and 10 mug . kg(-1) . min(-1) (5.5+/-0.5 and 6.1+/-0.7 versus 4.5+/-5.2 L/min at baseline), but the increase in renal blood flow appeared proportionately larger than corresponding increases in cardiac output. CONCLUSIONS: Dopamine is associated with an increase in renal blood flow in patients with heart failure. This effect is due to dilation of both the large conductance and small resistance renal blood vessels. Further evaluation of the efficacy and safety of dopamine for improvement of renal function in hospitalized patients with heart failure is warranted.