['To determine the acute effects of type 5 phosphodiesterase inhibition with sildenafil on flow-mediated vasodilation in the brachial artery of patients with chronic heart failure.', 'Impaired endothelium-dependent, flow-mediated vasodilation in patients with heart failure is partly attributable to hyporesponsiveness of cyclic guanosine monophosphate (cGMP) mediated vasorelaxation effector mechanisms in vascular smooth muscle. The effect of inhibition of cGMP degradation with sildenafil, a specific type 5 cGMP phosphodiesterase inhibitor, on flow-mediated dilation in heart failure is unknown.', 'Flow-mediated vasodilation after release of 1, 3 and 5 min of transient arterial occlusion was measured in the brachial artery with high resolution two-dimensional ultrasound imaging in 48 patients with chronic heart failure before and 1 h after randomized, double-blind assignment to a single oral dose of sildenafil 12.5, 25 or 50 mg or matching placebo.', 'In response to oral administration of a single dose of study drug, the change in flow-mediated vasodilation after release of 1, 3 and 5 min of arterial occlusion was significantly greater in patients receiving sildenafil 25 mg (3.3 +/- 1.9, 3.8 +/- 1.8 and 4.0 +/- 1.8%, respectively, p < 0.05) and patients receiving sildenafil 50 mg (3.7 +/- 1.3, 4.1 +/- 1.1, 3.9 +/- 1.3%, respectively, p < 0.05) than that of patients receiving placebo (0.7 +/- 1.1, 0.2 +/- 1.2, 0.6 +/- 0.8%, respectively).'] Does acute type 5 phosphodiesterase inhibition with sildenafil enhance flow-mediated vasodilation in patients with chronic heart failure?