Pharmacokinetic/Pharmacodynamic Study of Udenafil in Adolescents

A dose escalation trial to determine the pharmacokinetics, safety and tolerance of udenafil in male and female adolescent subjects with single ventricle physiology that that have undergone the Fontan surgical procedure. Pharmacodynamic data will also be collected to evaluate the effect of udenafil on acute exercise performance, peripheral vascular function and indices of myocardial performance. Five udenafil cohorts will be evaluated in additional to one drug free cohort