 For infants and newborns who have a heart defect at birth that leaves them with one functional ventricle, there is a series of surgeries that are required to allow survival. These surgeries ultimately lead to a common heart and great blood vessel circulation called a cavopulmonary anastomosis Fontan. This has allowed for survival into adulthood from universally fatal outcome in infancy. However, the non-physiologic blood flow patterns of the Fontan pathway do result in certain complications, including protein losing enteropathy PLE, which occurs in 3.7-13.4 of patients. PLE is denoted by the loss of protein, fats, and other key nutrients into the intestines, which can lead to significant morbidity. Recent evidence suggests that this is in part mediated by impaired flow of lymph from the intestines, which is carried by the parallel vascular system called the lymphatic system. Lymphatics return these nutrients and the fluid that leaks out of the blood vessels throughout the body back into the blood circulatory system by functioning as a series of pumps with one-way valves. While few treatments exist from PLE, evidence demonstrates continuous infusion of dopamine can help resolve PLE symptoms. Studies of isolated lymphatic vessels demonstrate that dopamine may increase the ability of lymphatic vessels to pump harder. This suggests the mechanism of action of dopamine in PLE is increasing the return of lymph in the non-physiologic blood flow patterns of Fontan patients. However, the link between improved return of lymph and improvement in PLE has not been established. Therefore, the investigators have designed this study to test whether markers of lymphatic flow and heart pump function improve when patients start continuous dopamine therapy a standard practice at the University of Michigan for PLE. This involves tracking markers of lymphatic recirculation through serial testing of blood and monitoring of PLE symptoms before and after the start of dopamine and other standard of care therapies. From these data, the investigators will correlate the monitored changes in lymph recirculation with changes in PLE symptoms. 