Fuel OLE Study of Udenafil After Fontan Treatment - Clinical Trial

We are doing this study is to learn whether children who have had the Fontan operation can improve their ability to exercise by taking the study medicine called Udenafil.

Single Ventricle Physiology after Fontan Palliation

Children who:
- Are between the ages of 12 and 19 years old.  
- Have Fontan physiology.
- Weigh more than 40kg (about 88 pounds).
- Are taller than 132cm (about 52 inches). 

If you would like for your child to be part of this study, your child will:
- Be involved in the study for about 15 months.
- Be given the study medicine, Udenafil.
- Have 2 in-person visits.
- Have 16 brief phone calls over 15 months.
- Be asked to do the following tests: Physical Exam, blood test, echocardiogram, exercise test, resting lung test, and electrocardiogram.