 Patients that have undergone a Fontan procedure surgical correction for single ventricle congenital heart disease may develop a complication known as protein-losing enteropathy PLE. Some studies suggest PLE is primarily caused by impaired lymph flow. Use of continuous dopamine infusion can improve PLE. Evidence suggests the effect of dopamine may be through its effect on lymphatic function. This study looks at markers of lymph flow and PLE symptoms after treatment using dopamine and other standard therapies during disease exacerbations. 