To elucidate the relation between exercise capacity and peripheral hemodynamics in patients after the Fontan operation, near-infrared spectroscopy was performed on the vastus lateralis muscle, and flow-mediated vasodilation of the brachial and posterior tibial arteries was done with high-resolution ultrasonography. In Fontan patients, diminished exercise capacity was related to a reduced blood flow supply and an attenuated post-exercise oxygen resaturation of the working skeletal muscle, which also was related to impaired endothelium-dependent vasodilation.