Fontan-palliated patients comprise an interesting group of single-ventricle patients who are dependent upon passive return of blood from the body to the lungs. Systemic venous pressures are therefore quite elevated, and one study demonstrated that venous capacitance was diminished. In addition, these patients have markedly diminished aerobic capacity (Max VO2). Although one recent study demonstrated that Fontan patients can increase their Max VO2 through diligent cardiac rehabilitation, their ultimate results were still well below average.

It has previously been described that normal, healthy subjects have decreased exercise performance in a supine vs upright position. However, due to high venous pressures and the need for systemic venous return to overcome gravity in order to perfuse the lungs, one might hypothesize that Fontan patients would have increased exercise performance in a supine vs upright position. The investigators are interested in studying this hypothesis.