Aim #1: Define and determine the prevalence of pulmonary vascular disease and diastolic dysfunction as assessed by the gold standard of invasive hemodynamic cardiopulmonary exercise testing.

Aim #2: Determine the role of rest-exercise echocardiography for the assessment hemodynamics in Fontan physiology.

Aim #3: Evaluate the clinical impact of pulmonary vascular disease and ventricular diastolic dysfunction.

Define and determine the prevalence of pulmonary vascular disease and diastolic dysfunction as assessed by the gold standard of invasive hemodynamic cardiopulmonary exercise testing. Subjects with Fontan palliation will undergo cardiac catheterization during exercise. The investigators hypothesize that invasive hemodynamic assessment during supine exercise will enable identification of early stage pulmonary vascular disease and diastolic dysfunction that is not apparent from invasive studies performed at rest.

Determine the role of rest-exercise echocardiography for the assessment hemodynamics in Fontan physiology. Transthoracic echocardiography will be performed at rest and during exercise simultaneously with catheterization in the subjects participating in Aim #1 to determine correlations between invasive and noninvasive hemodynamics and identify noninvasive alternatives to assess functional reserve.

Evaluate the clinical impact of pulmonary vascular disease and ventricular diastolic dysfunction. Multi-organ function and patient reported outcomes will be evaluated at baseline, 12 months (optional), and 24 months (optional) in subjects participating in Aims #1 and #2. The investigators hypothesize that subjects with poorer ventricular-vascular reserve will display more clinical and end-organ deterioration in longitudinal follow up.

Inclusion Criteria:

• Fontan Palliation
• Age ≥18 years

Exclusion Criteria:

-No clinical indication for cardiac catheterization

Fontan palliation