Consistent with our Aims and Hypotheses, four patient groups will be studied: i)Fontan Physiology Patients with PLE and PB Patients ii) Fontan Physiology Patients without PLE and PB iii) Patients with Glenn Physiology Congenital Heart Disease and iv) Patients with 2 ventricle physiology and an atrial septal defect who will serve as a Control group. Measurement of mixed venous and arterial levels of substance P and VIP in these 4 groups of subjects will allow us to determine the effects of elevated portal venous pressure on the production and clearance of substance P and VIP and well as the effects of altered hepatic-pulmonary blood flow on the clearance of substance P and VIP. This should allow us to determine if 1) systemic arterial levels of substance P and VIP levels are elevated in Fontan patients when compared to controls, and if elevated, 2) whether this is due to increased hepatic production, reduced pulmonary clearance or both. The rationale for the inclusion of each patient group is summarized below.