Truncus arteriosus is a rare heart defect that's present at birth (congenital). This condition means that one large blood vessel leads out of the heart. Learn more about this congenital disease. Fontan Palliation Fontan operation (palliation) is a complex open heart surgery that is often performed in multiple stages. It is designed to treat patients with complex congenital heart disease known as a single ventricle. In patients with single ventricle, oxygen-poor blood that should go to the lungs and oxygen-rich blood that should go to the rest of the body are mixed together and this creates severe circulatory problems. The Fontan operation is designed to direct oxygen-poor blood to the lungs, and oxygen-rich blood to the body. Adults who have undergone prior Fontan operation have reduced survival compared to people without heart disease. This is because these patients are prone to several complications such as heart failure, abnormal heart rhythm (arrhythmia), liver disease, kidney disease, high risk of blood clot, protein-losing enteropathy (disease of the gut) and several other problems. The Mayo Clinic was one of the first hospitals to perform the Fontan operation in North America, and as a result the doctors at Mayo Clinic have a lot of experience caring for these patients. All adults who have a Fontan operation require lifelong follow-up at a specialized center such as the Mayo Clinic because of the multiple complications to which these patients are prone.