The Hemodynamic Effects of Vasopressin in Patients With Fontan Physiology

The goal of this study is to evaluate if vasopressin can elevate systemic arterial blood pressures without having a significant effect on pulmonary arterial pressures. Because patients who have undergone Fontan procedures rely on low pressures across the pulmonary vascular bed to maintain cardiac output, vasoactive agents that concomitantly increase systemic and pulmonary pressures may have a deleterious effect in this specific patient population. Hypothesis: In patients with Fontan physiology, vasopressin will increase systemic BP by 20% above baseline, without increasing the transpulmonary gradient.