Simple Non-invasive Breathing Device to Improve Pulmonary Flow Pusatility in Single Ventricle Post Fontan

This is a pilot study using a novel, minimal risk, portable, hands-free oral-positive pressure device (oPEP) in patients with Fontan palliation that will examine whether using this device in both the acute and chronic phase will alter Fontan hemodynamics and create pulsatility in the Fontan circuit and thereby increasing cardiac output. This device is easy to use and poses no significant risk to human subjects. The investigators will measure this through echocardiographic measures including pulsatility in different aspects of the Fontan circuit including IVC, hepatic veins, the Fontan conduit, and pulmonary arteries and aortic blood flow measurements. After demonstration of how to use the device appropriately, the investigators will have patients use the device after their clinical echocardiogram for their clinic appointment. The investigators will ask them to use the device at home 3-4 times a day for 10-15 mins and have them return in approximately 4 weeks to have another echocardiogram done with the same measurements.