Today, we try to offer a Fontan procedure to all children who are born with abnormal hearts that cannot be repaired with two pumping chambers (ventricles). One pumping chamber, the left ventricle, pushes the blood to the body, and the other, the right ventricle, pushes the blood to the lungs. Sometimes, these children are completely missing a ventricle and have what is called a single ventricle. Often, there are two ventricles, but one of them is too small to be really useful. At times, there are two good ventricles with some holes, but the connections between the ventricles and the collecting chambers and/or the vessels going to and out of the heart is so abnormal that it is impossible to close these holes and use separately the two ventricles. After the Fontan, all these children are said to have the heart functioning with a single pumping chamber, and we say that they have a "functional single ventricle". There are many different condition of the heart that necessitates a Fontan procedure. The most frequent ones are called:

• Tricuspid atresia,
• Hypoplastic left heart syndrome
• Unbalanced atrio-ventricular septal defect
• Double outlet right ventricle
• Double inlet left ventricle
• Pulmonary atresia with intact ventricular septum