Fontan Udenafil Exercise Longitudinal Assessment Trial - 2

Inclusion Criteria:

1. Males and females with Fontan physiology who are 12 to less than 19 years of age atenrollment.

2. Participant consent or parental/guardian consent and participant assent.

3. Participant fluency in primary language of country in which study is beingconducted.

4. Current antiplatelet or anticoagulant therapy.

Exclusion Criteria:

1. Height < 132 cm.

2. Weight < 40 kg.

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 veinstenosis resulting in a mean gradient of > 4 mmHg between the regions proximal anddistal 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. Failure to achieve maximal exertion (defined as RER < 1.10) on screening/baselineexercise test.

10. Peak minute oxygen consumption (VO2) less than 45% or ≥ 80% of predicated for ageand gender at enrollment.

11. Severe ventricular dysfunction assessed qualitatively by clinical echocardiographywithin 6 months prior to enrollment.

12. Severe valvar regurgitation, ventricular outflow obstruction, or severe aortic archobstruction assessed by clinical echocardiography within six months prior toenrollment.

13. History of significant renal (serum creatinine > 2.0), hepatic (serum AST and/or ALT > 3 times upper limit of normal), gastrointestinal or biliary disorders that couldimpair absorption, metabolism or excretion of orally administered medications.

14. Inability to complete exercise testing at baseline screening.

15. Subjects with a pacemaker whose heart rate at peak exercise is controlled by theextrinsic pacemaker as opposed to a native atrial rhythm.

16. History of PDE-5 inhibitor use within 12 months prior to enrollment. (Treatment isdefined as chronic therapy as opposed to a single dose.)

17. History of any other medication for treatment of pulmonary hypertension within 3months before study onset.

18. Known intolerance to oral udenafil.

19. Frequent use of medications or other substances that inhibit or induce CYP3A4.

20. Current use of alpha-blockers or nitrates.

21. Ongoing or planned participation in another research protocol that would eitherprevent successful completion of planned study testing or invalidate its results.

22. Noncardiac medical, psychiatric, and/or social disorder that would preventsuccessful completion of planned study testing or would invalidate its results.

23. Cardiac care, ongoing or planned, at a non-study center that would impede studycompletion.

24. For females: Pregnancy at the time of screening, pregnancy planned before studycompletion, or refusal to use an acceptable method of contraception for studyduration if sexually active.

25. Unable to abstain or limit intake of grapefruit juice and grapefruit containingdrinks during the duration of the trial.

26. Refusal to provide written informed consent/assent.

27. In the opinion of the investigator, the subject is likely to be non-compliant withthe study protocol.

28. History of clinically significant thromboembolic event, in the option of the sitePrincipal Investigator, that may put the subject at increased risk of a subsequentevent while participating in the study.

29. Coronavirus disease 2019 (COVID-19) vaccination or symptoms of COVID-19 infectionwithin 7 days of Visit 1.

30. Not taking antiplatelet or anticoagulant therapy.