The Fontan is a heart surgery for children born with only one working pumping chamber instead of the usual two. In a typical heart, one chamber pumps blood to the lungs and the other pumps it to the body. When one of those chambers is missing or too small to function, surgeons use the Fontan procedure to reroute blood flow so that a single chamber can do the work of both. It’s not a cure, but it allows children with otherwise life-threatening heart defects to survive and grow into adulthood.
Why Some Children Need a Fontan
A normal heart has four chambers: two upper (atria) and two lower (ventricles). The right ventricle pumps blood to the lungs to pick up oxygen, and the left ventricle pumps oxygen-rich blood out to the body. In some babies, one ventricle never develops properly. This is called single-ventricle physiology, and it can result from several different birth defects.
The most common is hypoplastic left heart syndrome, where the left side of the heart is severely underdeveloped. Other conditions include tricuspid atresia (a missing or blocked valve on the right side), double-inlet left ventricle, and pulmonary atresia with an intact wall between the ventricles. In all of these, the baby is left with only one ventricle capable of pumping blood effectively. Without surgical intervention, these defects are fatal.
The Three Stages of Surgery
The Fontan isn’t a single operation. It’s the final step in a series of three surgeries performed over the first few years of life, each one gradually restructuring the circulation.
- Stage 1: Norwood procedure. Performed within the first few days after birth, this surgery creates a temporary pathway so the single ventricle can pump blood to both the lungs and the body.
- Stage 2: Glenn or hemi-Fontan. Done around six months of age, this connects the large vein carrying blood from the upper body directly to the lung arteries, reducing the workload on the single ventricle.
- Stage 3: Fontan completion. Performed between roughly 18 months and 3 years of age, this final surgery connects the large vein from the lower body to the lung arteries as well, completing the reroute.
After the Fontan is complete, all the oxygen-poor blood returning from the body flows passively into the lungs without being pumped by a ventricle. The single remaining ventricle is dedicated entirely to pumping oxygen-rich blood out to the body.
How Fontan Circulation Works
In a normal heart, the right ventricle actively pushes blood through the lungs. In a Fontan circulation, there is no pump driving blood into the lung arteries. Instead, the systemic veins are connected directly to the pulmonary arteries, and blood moves through the lungs using only the residual pressure left over after it has traveled through the body’s capillaries. Think of it as coasting downhill: the blood has just enough momentum from the previous pump cycle to squeeze through the lungs and return to the heart.
This passive flow is the defining feature of Fontan circulation, and it’s also the source of most long-term challenges. Because no ventricle is pushing blood through the lungs, venous pressure throughout the body stays higher than normal. That elevated pressure affects the liver, the gut, and the lymphatic system over time. The single ventricle, meanwhile, cannot compensate by “pulling” blood through the lungs with suction. The system works, but with narrow margins.
Two Main Surgical Techniques
Surgeons complete the Fontan using one of two approaches. In the lateral tunnel technique, a baffle (a kind of internal partition) is created inside the right atrium to channel blood from the lower body vein to the lung arteries. In the extracardiac conduit technique, an artificial tube is placed outside the heart to make the same connection without opening the heart chamber at all.
The extracardiac approach has become more widely favored. Because the heart doesn’t need to be opened, time on the heart-lung bypass machine is shorter and the heart spends less time without blood flow. One study found that the heart was without circulation for an average of 4 minutes with the extracardiac method compared to 48 minutes with the lateral tunnel. The extracardiac conduit also carries a lower risk of abnormal heart rhythms: at six years of follow-up, 92% of extracardiac patients remained free of arrhythmias compared to 83% with the lateral tunnel.
Long-Term Survival
Survival after the Fontan has improved considerably since the procedure was first performed in 1971, but it remains a palliative surgery, meaning it manages the condition rather than fully correcting it. Data from the Korean Fontan Registry shows overall survival rates of about 92% at 10 years, 87% at 20 years, and 74% at 30 years after surgery. These numbers reflect patients operated on across several decades, including earlier eras when techniques were less refined. Children undergoing the Fontan today generally have better outcomes than these historical averages suggest.
Liver Disease After Fontan
Fontan-associated liver disease is one of the most significant long-term complications and develops in virtually all patients to some degree. The elevated venous pressure inherent to Fontan circulation causes chronic congestion in the liver, similar to what happens when water backs up behind a dam. Over years and decades, this congestion leads to scarring (fibrosis) and eventually cirrhosis in some patients.
The challenge is that liver damage from Fontan circulation progresses silently. Blood tests often remain near-normal until the disease is advanced. For this reason, regular imaging is a key part of lifelong monitoring. In later stages, complications can include fluid buildup in the abdomen, bleeding from swollen veins in the esophagus, and jaundice. Because advanced liver disease carries a 15 to 20 percent mortality risk from certain complications, screening with endoscopy is commonly recommended for adult Fontan patients who show signs of significant scarring. Some patients ultimately need both a heart and liver transplant.
Protein-Losing Enteropathy
Between 5 and 12 percent of Fontan patients develop a condition called protein-losing enteropathy, or PLE, in which protein leaks from the gut lining into the intestines and is lost from the body. The high venous pressure in Fontan circulation causes the lymphatic vessels in the gut wall to become congested and swollen, eventually spilling protein-rich lymph fluid into the intestine. Low cardiac output can also reduce blood flow to the intestinal lining, making it more permeable.
The resulting protein loss drops the levels of albumin in the blood, which normally helps hold fluid inside blood vessels. Without enough albumin, fluid leaks into tissues, causing swelling in the legs, fluid in the abdomen, and sometimes fluid around the lungs or heart. Patients often experience chronic or intermittent diarrhea, bloating, and abdominal pain. PLE is one of the more serious complications of Fontan circulation and is associated with significantly worse outcomes.
Exercise and Daily Life
People living with a Fontan circulation have lower exercise capacity than their peers. Studies of young Fontan patients show peak oxygen uptake averaging about 61% of normal values. In practical terms, 68% of Fontan patients in one study reported that running was noticeably harder and slower for them compared to peers, with shortness of breath being the most commonly reported limitation.
Despite these limits, regular physical activity is both safe and beneficial. The Fontan circulation was designed to support everyday activities, even if reserves for intense effort are limited. A six-month individualized exercise program in young Fontan patients improved both peak oxygen uptake and the point at which muscles switch to less efficient energy production. Most everyday activities fall within the aerobic range that Fontan patients can comfortably sustain. Exercise counseling from a medical team familiar with congenital heart disease helps patients find the right balance between staying active and respecting their body’s limits.
Pregnancy With a Fontan
Pregnancy is possible for women with Fontan circulation, but it carries substantially higher risks than in the general population. A large review of 400 pregnant women with Fontan circulation and over 1,200 pregnancies found a miscarriage rate of about 41%, roughly double the general population rate. Among pregnancies that continued, 57% resulted in preterm delivery and about 21% of babies were smaller than expected for their gestational age.
Maternal complications included heart rhythm disturbances in about 7% of pregnancies and heart failure in nearly 4%. About 12% experienced significant bleeding after delivery. On a reassuring note, no maternal deaths were reported across the studies reviewed, and the rate of the baby being born with a heart defect was low at about 1.4%. Roughly half of deliveries were by cesarean section. For women considering pregnancy, pre-conception planning with a team experienced in adult congenital heart disease is essential for managing these risks.
Blood Clot Prevention
The sluggish, passive blood flow through a Fontan circuit creates an elevated risk of blood clots. Most Fontan patients take some form of blood-thinning medication for life. The American College of Cardiology outlines a risk-based approach: patients at low risk for clots typically take aspirin alone, while those with additional risk factors such as irregular heart rhythms, a history of prior clots, or significantly reduced heart function are treated with stronger anticoagulants. Newer oral anticoagulants have emerged as an option that avoids the frequent blood testing and dietary restrictions associated with older medications like warfarin, though both remain effective choices depending on the individual’s risk profile.