Fontan Udenafil Exercise Longitudinal Assessment Trial (FUEL-2)

This study is a 26 week, prospective, multicenter, randomized, double-blinded, placebo-controlled safety and efficacy study of udenafil vs. placebo in adolescent subjects who have had the Fontan procedure. The primary efficacy endpoint will be change from baseline at 26 weeks in peak minute oxygen consumption (VO2 mL/kg/min) as measured by maximal cardiopulmonary exercise test (CPET) reading laboratory who will be blinded to treatment allocation.