In the present study we proposed to examine neo-aortic properties in a cohort of children with single ventricle heart defects who have undergone the bi-directional Glenn procedure (with or without Norwood palliation) and compare them to a cohort of patients with single ventricle who have had no aortic arch interventions. Patients in both groups typically undergo the Fontan operation between 18-48 months of age. After arrival to the operating suite and the placement of routine instrumentation, a transesophageal echocardiography (TEE) is routinely obtained. All data needed for this protocol is obtained during this TEE.