Jane Newburger, MD, Associate Cardiologist-in-Chief at Children's Hospital Boston offered the following responses:

What is a Fontan procedure?

Let me begin by noting that cyanotic or "right to left shunt" heart problems represent a more severe and complex group of congenital pediatric heart disease. These complicated heart defects involve structural changes in the cardiovascular system that result in blood being shunted away from the lungs (right side) toward the body (left side). As a result, these youngsters have lower levels of oxygen in their blood causing cyanosis evidenced by the "blueness of their lips and finger nails." In some of these complex lesions, children have only a single working pumping chamber (single ventricle). The Fontan operation represents a surgical advance in trying to help this group of children. It is an operation designed to more closely approximate normal blood circulation in which the "red" (oxygenated) blood is separated from the "blue" (less oxygenated) blood, Restated, a Fontan operation is used to separate "red" and "blue" blood in children who have only a single working pumping chamber. The exact "plumbing" of the Fontan circuit varies depending upon the type of single ventricle defect, but the following basic principles are always the same:

• "Blue" blood returning from the veins of the body is directed into the lung arteries without ever passing through a ventricle.

• The flow of "blue" blood into the lungs relies on very low resistance to flow into the lungs.

• "Red" blood then returns from the lungs to the atria and then through valves to reach the single ventricle.

• From the single ventricle, red blood is pumped out to the body in the aorta.

In order for the Fontan circuit to work well, the resistance in the blood vessels of the lungs must remain low. Higher resistance and hence trouble with the circuit can result when the muscle of the single ventricle becomes weak, when valves develop leaks, or when blood vessels develop blockages.

Almost all individuals who have had a Fontan operation eventually develop some problems with the electrical circuits inside the heart. We have many good treatments for these problems, both using medicines and using radiofrequency ablation, in which we "zap" short circuits and thereby make fast heart rhythms less common.

Children and adults who have had Fontan procedures are also prone to developing blood clots in the heart. To reduce the likelihood of such blood clots, we always use either aspirin or blood thinners in patients who have had the Fontan operation.

I always explain that a Fontan operation does not cure congenital heart disease. It is very unlikely that an individual who has had a Fontan procedure will be an Olympic athlete; nevertheless, exercise ability is good enough to allow participation in usual daily activities. Most individuals who have had a Fontan procedure are successful in leading a relatively normal life. For those rare individuals for whom the Fontan procedure is performed but ultimately doesn't work as well as it should, heart transplantation is an option.

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