The Fontan procedure’s main benefit is to infants with serious congenital heart defects that reduce the amount of oxygen-rich blood being pumped to the body. In these cases, the Fontan allows surgeons to bypass the right side of the heart and send oxygen-poor blood directly to the lungs. The right ventricle may then be pressed into service as the heart’s main pumping chamber, sending oxygen-rich blood to the tissues and organs of the body. The procedure is also valuable in patients whose right side of the heart is malfunctioning for some reason, whether or not the left ventricle is involved.

In general, the Fontan is less risky for patients who have fewer heart defects. Ideally, the patient has a normal pulmonary artery, normal drainage of oxygen-poor blood from the veins into the heart, normal pumping ability of the ventricles, normal heart rhythm, a normal-sized right atrium and so forth. The surgeon needs to know as much as possible about other heart defects that may be present before surgery begins.

However, even under ideal circumstances, the Fontan is complicated and carries a number of risks to the young patient. These risks include:

• Formation of blood clots. Because the surgery currently involves the use of foreign materials to create new passageways, there is a risk of blood clots forming in and around those foreign materials. To reduce the risk of blood clots, patients are generally prescribed daily aspirin and/or anticoagulants for months after surgery and often continue taking aspirin for life. Researchers are developing strategies for performing the Fontan without using foreign materials.