Table 1.

FUEL Inclusion and Exclusion Criteria

Inclusion Criteria
1	Males and females with Fontan physiology 12 – <19 years of age at enrollment
2	Participant consent or parental/guardian consent with participant assent
3	Participant fluent in English, Spanish, or Korean
Exclusion Criteria
1	Weight <40 kg
2	Height <132 cm
3	Hospitalization for acute decompensated heart failure within the last 12 months
4	Current intravenous inotropic drugs
5	Undergoing evaluation for heart transplantation or listed for transplantation
6	Diagnosis of active protein losing enteropathy or plastic bronchitis within the last 3 years, or a history of liver cirrhosis
7	Known Fontan baffle obstruction, branch pulmonary artery stenosis, or pulmonary vein stenosis resulting in a mean gradient of >4 mmHg between the regions proximal and distal to the obstruction as measured by either catheterization or echocardiography, obtained prior to screening for the trial
8	Single lung physiology with greater than 80% flow to one lung
9	VO2 max less than 50% of predicted for age and gender at enrollment
10	Severe ventricular dysfunction assessed qualitatively by clinical echocardiography within six months prior to enrollment
11	Severe valve regurgitation, ventricular outflow obstruction, or aortic arch obstruction assessed by clinical echocardiography within six months prior to enrollment
12	Significant renal (serum creatinine >2.0), hepatic (serum AST and/or ALT >3 times upper limit of normal), gastrointestinal or biliary disorders that could impair absorption, metabolism or excretion of orally administered medications, based on laboratory assessment six weeks prior to screening for the trial
13	Inability to complete exercise testing at baseline screening
14	History of PDE-5 inhibitor use within 3 months before study onset
15	History of any other medication for treatment of pulmonary hypertension within 3 months before study onset
16	Known intolerance to oral udenafil
17	Frequent use of medications or other substances that inhibit or induce CYP3A4
18	Current use of alpha-blockers or nitrates
19	Ongoing or planned participation in another research protocol that would either prevent successful completion of planned study testing or invalidate its results
20	Non-cardiac medical, psychiatric, and/or social disorder that would prevent successful completion of planned study testing or would invalidate its results
21	Cardiac care, ongoing or planned, at a non-study center that would impede study completion
22	For females: pregnancy at the time of screening, pregnancy planned before study completion, or refusal to use an acceptable method of contraception for study duration if sexually active
23	Inability to abstain from or limit intake of grapefruit juice during the duration of the trial
24	Refusal to provide written informed consent/assent
25	In the opinion of the primary care physician, the subject is likely to be non-compliant with the study protocol

ALT – alanine aminotransferase; AST – aspartate aminotransferase; PDE-5 – phosphodiesterase type 5; CYP3A4 – cytochrome P450 3A4; VO2 max – maximal oxygen consumption