The Fontan procedure is a surgery that reroutes blood flow in children born with only one working heart ventricle instead of the usual two. Rather than repairing the heart to function normally, it reconfigures the plumbing so that oxygen-poor blood flows passively to the lungs without being pumped by a ventricle, while the single functioning ventricle handles all the work of pushing oxygenated blood to the body. It is not a cure but a lifelong palliation, and the resulting circulation creates a distinctive set of consequences that touch nearly every organ system over time.
Who Needs the Fontan
A normal heart has two ventricles: one pumps blood to the lungs, the other to the body. Some babies are born with defects so severe that only one ventricle can do useful work. The specific diagnoses vary and include tricuspid atresia, hypoplastic left heart syndrome, double-inlet ventricle, and pulmonary atresia with an intact ventricular septum, among others.1PubMed. The Fontan procedure: anatomy, complications, and manifestations of failure What unites them is that two-ventricle repair is not feasible. Any patient with only one functioning ventricle is a candidate for the Fontan pathway.2PubMed. Fontan Operation: Indications, Short and Long Term Outcomes
The Fontan is not performed in a single operation. It is the final stage of a series of surgeries, typically completed between ages two and four. Before the Fontan itself, most children undergo at least one preliminary procedure, often a bidirectional Glenn shunt that connects the upper body’s veins directly to the pulmonary arteries.3PubMed Central. Fontan completion after Norwood with bidirectional Glenn shunt: their haemodynamics and pulmonary artery configuration Children with hypoplastic left heart syndrome usually require an additional earlier operation (the Norwood) within the first days of life. Each stage gradually transitions the body toward the final Fontan circulation.
How Blood Flows Without a Pump
In a Fontan circulation, the veins returning blood from the body are connected directly to the pulmonary arteries. There is no ventricle pushing that blood through the lungs. Instead, blood moves through the lungs passively, driven by the small pressure difference between the veins and the left side of the heart. This is fundamentally different from normal physiology, and three characteristics define it: elevated pressure in the body’s veins, low and non-pulsatile blood flow through the lungs, and reduced overall cardiac output.4PubMed. The Fontan Circulation: From Ideal to Failing Hemodynamics and Drug Therapies for Optimization
Because there is no pump for the lungs, the system is heavily dependent on how easily blood can pass through the pulmonary vessels. Resistance in those vessels is the single most important factor governing how much blood the heart can ultimately deliver to the body. Computational modeling has shown that pulmonary vascular resistance, how well the ventricle relaxes to fill, and the flexibility of the body’s blood vessels all play major roles, while heart rate and the strength of the ventricle’s squeeze are secondary.5PubMed. Hemodynamic performance of the Fontan circulation compared with a normal biventricular circulation: a computational model study In practical terms, anything that raises resistance in the lung vessels, whether infection, blood clots, or simply aging, can significantly reduce how well the circulation performs.
The necessary trade-off of the Fontan is chronically elevated venous pressure. A strong correlation exists between central venous pressure and pulmonary vascular resistance in Fontan patients, a relationship not seen in people with normal hearts.6PubMed Central. Venous Congestion and Pulmonary Vascular Function in Fontan Circulation: Implications for Prognosis and Treatment That elevated back-pressure on the veins is what drives many of the organ complications discussed below.
The Fenestration Debate
During surgery, many surgeons create a small hole, called a fenestration, between the Fontan circuit and the heart’s atrium. This acts as a pressure-relief valve: it lets a small amount of oxygen-poor blood bypass the lungs and mix with oxygenated blood, which lowers venous pressure and helps maintain cardiac output. The trade-off is a modest drop in oxygen levels.7PubMed. Transcatheter Fontan Fenestration Closure: Sustained Improvements in Oxygen Saturation with Minimal Morbidity and Mortality The fenestration can later be closed with a catheter-based device when the body has adjusted.
Whether closing the fenestration meaningfully changes exercise performance is less clear than you might expect. When researchers have compared Fontan patients with and without a fenestration, they have found no significant differences in exercise time or how the body extracts and uses oxygen during exertion.8PubMed. Effect of Fontan fenestration on regional venous oxygen saturation during exercise: further insights into Fontan fenestration closure The decision to fenestrate is often made based on the patient’s hemodynamics at the time of surgery rather than a universal protocol.
Survival and Surgical Outcomes
The Fontan procedure has improved dramatically since its introduction in the 1970s. Modern iterations, particularly the lateral tunnel and extracardiac conduit techniques, carry an operative mortality around 5%. Reported five-year survival for the lateral tunnel approach is roughly 93%, dropping to about 91% at ten years.9Elsevier. The Lateral Tunnel Fontan These numbers represent a remarkable achievement for a condition that was uniformly fatal before surgical intervention existed. But survival statistics only tell part of the story. Living with a Fontan circulation means managing a body whose hemodynamics are inherently abnormal, and complications accumulate with time.
Liver Disease After the Fontan
Fontan-associated liver disease, or FALD, is nearly universal. Surveillance biopsies have shown that virtually all Fontan patients develop silent liver fibrosis by adolescence.10PubMed Central. Fontan-Associated Liver Disease: Screening, Management, and Transplant Considerations The mechanism is straightforward in concept: chronically elevated venous pressure backs up into the liver, creating persistent congestion. Combined with reduced cardiac output, this produces a distinctive type of congestive liver injury driven by multiple overlapping factors.11PubMed Central. Fontan-associated liver disease: Diagnosis, surveillance, and management
Monitoring FALD is tricky. Standard tools used for other liver diseases do not always work well here. MR elastography, for instance, measures how stiff the liver is, but in Fontan patients the congestion itself raises stiffness independently of fibrosis, making it difficult to determine how much damage is actually due to scarring versus ongoing congestion.12PubMed. MR elastography-based staging of liver fibrosis in Fontan procedure associated liver disease is confounded by effects of venous congestion Researchers are working on better imaging biomarkers, but for now, tracking liver stiffness over time remains the most practical approach, even if any single measurement is hard to interpret in isolation.
In some patients, FALD progresses to cirrhosis and even liver cancer, leading to increasing reports of combined heart-liver transplantation as the Fontan population ages.
Gut Problems and Protein Loss
The same venous congestion that damages the liver also affects the gut. Protein-losing enteropathy, or PLE, occurs when the intestinal lining leaks proteins into the bowel. It is a feared complication because it causes swelling, malnutrition, and immune problems. Elevated central venous pressure drives both hepatic and intestinal congestion, setting the stage for PLE.13PubMed. Protein-losing enteropathy and the Fontan operation The exact trigger that tips some patients from congestion into full-blown protein loss remains poorly understood, though abnormal mesenteric vascular resistance and inflammation appear to play roles.14PubMed. Protein-losing enteropathy after fontan operation: investigations into possible pathophysiologic mechanisms
PLE and advanced liver disease tend to travel together. Patients with PLE show higher liver stiffness, more signs of portal hypertension such as enlarged spleens and esophageal varices, and elevated markers of systemic inflammation.15PubMed. Fontan protein-losing enteropathy is associated with advanced liver disease and a proinflammatory intestinal and systemic state This overlap makes treatment challenging, since targeting one organ system rarely addresses the underlying hemodynamic problem.
Plastic bronchitis is a related complication affecting the airways rather than the gut. It occurs in roughly 4% of Fontan patients, typically within a few years of surgery, and involves rubbery casts of protein that form in the bronchial tree and can cause coughing, wheezing, or in severe cases, airway obstruction. Both PLE and plastic bronchitis share a root cause in lymphatic system disruption: elevated venous pressure overwhelms the lymphatic drainage, causing lymph to leak into low-pressure spaces like the intestines or airways.16PubMed. Plastic Bronchitis and Protein-Losing Enteropathy in the Fontan Patient: Evolving Understanding and Emerging Therapies
Heart Rhythm Problems
Arrhythmias are among the most common long-term complications, affecting roughly 15% to 60% of Fontan patients depending on age and how long they have lived with the circulation. The most frequent type is intra-atrial reentrant tachycardia, a fast rhythm caused by electrical signals looping within the atrial tissue.17PubMed Central. Atrial Arrhythmias in Adults with Fontan Palliation The combination of surgical scar tissue and chronically stretched atrial walls creates fertile ground for abnormal electrical circuits.
These rhythm problems are especially dangerous in the Fontan population because the circulation has so little hemodynamic reserve. A fast or irregular heart rhythm that a person with a normal heart might barely notice can cause significant drops in cardiac output in a Fontan patient. Treatment options include medications, pacemakers, and catheter ablation, but success rates for ablation of atrial flutter hover around 50% to 70%, with high recurrence rates regardless of which approach is used.18Seminars in Thoracic and Cardiovascular Surgery: Pediatric Cardiac Surgery Annual. Sinus Node Dysfunction and Atrial Tachycardia After the Fontan Procedure: The Scope of the Problem
Blood Clots and Prevention Strategies
Fontan patients are at high risk for blood clots. The sluggish, non-pulsatile flow through the circuit, combined with changes in clotting factors that come with chronic liver disease, creates a prothrombotic state. Almost all patients are placed on some form of blood-thinning therapy, but what type works best has been debated for decades.19PubMed Central. Thromboembolism and anticoagulation after Fontan surgery
A meta-analysis comparing strategies found that both aspirin and warfarin significantly reduced clot rates compared with no prevention, and there was no significant difference between the two.20Heart. Strategies for thromboprophylaxis in Fontan circulation: a meta-analysis More recent network analyses that include newer oral anticoagulants suggest these newer drugs may be the most effective at preventing clots, though aspirin tends to have the most favorable overall profile when bleeding risk is considered alongside clot prevention.21PubMed Central. Thromboprophylaxis in Patients With Fontan Circulation The field still lacks a definitive large randomized trial, so practice varies between centers.
Exercise and Physical Activity
Fontan patients consistently show reduced exercise capacity compared with healthy peers. The low cardiac output and inability to adequately increase blood flow to working muscles during exertion set a ceiling on what the cardiovascular system can deliver. Reduced fitness is explained partly by the limited cardiorespiratory capacity and partly by changes in skeletal muscle function itself.22PubMed Central. Exercise capacity and impact of exercise training in patients after a Fontan procedure: a review
Despite these limitations, exercise training is safe and beneficial. A systematic review found that programs combining aerobic and resistance training, done about twice weekly under supervision, improved peak oxygen consumption and quality of life.23European Journal of Preventive Cardiology. Physical exercise training in patients with a Fontan circulation: A systematic review Pulmonary vasodilator medications may offer a modest additional boost in exercise capacity, but exercise training itself tends to produce a more consistent and larger effect.24PubMed Central. Exercise Pathophysiology and Testing in Individuals With a Fontan Circulation The takeaway for patients and families is that physical activity should be encouraged, not avoided.
Kidney Function Over Time
The kidneys are another organ quietly affected by Fontan physiology. In an adult Fontan cohort, kidney function declined at a faster rate than in healthy controls, losing an average of about 1.4 units of filtration capacity per year compared to roughly 0.9 in the general population, even though kidney function was approximately equal at the start of adulthood. Faster kidney decline was linked to higher levels of a heart failure marker (NT-proBNP), and each unit of kidney function lost was associated with a small but significant increase in mortality risk.25PubMed Central. Deterioration in Renal Function in Patients With a Fontan Circulation and Association With Mortality
Standard blood tests may underestimate the problem. Creatinine-based kidney estimates detected chronic kidney disease in only about 11% of Fontan patients, while a different marker called cystatin C detected it in 37%. The discrepancy likely stems from Fontan patients having lower muscle mass, which artificially lowers creatinine levels and makes kidney function look better than it is. Higher venous pressure and higher body fat were associated with markers of ongoing kidney injury.26PubMed Central. Associations Between Characteristics of Individuals With Fontan Circulation With Blood and Urine Biomarkers of Kidney Injury and Dysfunction
Brain Development and Cognition
Children who have undergone the Fontan pathway face neurodevelopmental challenges. In a study of over 200 children assessed around age five, average IQ was in the lower-normal range at about 93.5, significantly below the population average of 100. Roughly one in five children showed moderate cognitive impairment, and about 4% had severe impairment.27PubMed Central. Childhood Neurocognitive Outcomes in Patients With Fontan Circulation These outcomes are not unique to the Fontan specifically. When compared with children who had other forms of congenital heart disease requiring biventricular repair, Fontan survivors showed similar neurodevelopmental profiles across most domains, suggesting that the impact comes from the cumulative burden of complex heart disease and multiple surgeries rather than the Fontan operation alone.28PubMed Central. Neurodevelopmental outcomes in preschool survivors of the Fontan procedure
Brain MRI findings add another layer. Among Fontan patients at school age, those with abnormal brain MRI findings had significantly lower IQ scores (averaging about 85) compared with those whose scans were normal (averaging about 96).29European Journal of Cardio-Thoracic Surgery. Long-term neurodevelopmental outcome and serial cerebral magnetic resonance imaging assessment in Fontan patients at school age Early identification and educational support can make a meaningful difference for affected children.
Pregnancy With a Fontan Circulation
As more Fontan patients survive into adulthood, pregnancy has become a real consideration. A systematic review covering 255 pregnancies in 133 women found that only about 45% resulted in live births. Miscarriage was common, affecting roughly 45% of pregnancies, and among live births, about 59% were premature. No maternal deaths were reported, and cardiovascular complications such as arrhythmias and heart failure, while present, were generally manageable with standard treatment.30PubMed. Pregnancy in Women With a Fontan Circulation: A Systematic Review of the Literature
A smaller study from two Polish centers reported similar patterns: among 26 pregnancies, 11 ended in miscarriage and 15 resulted in 16 live births. Prematurity was the most frequent fetal complication, and obstetric complications occurred in 40% of completed pregnancies, including placental abruption and premature rupture of membranes. No mother experienced heart failure decompensation or died.31PubMed Central. Pregnancy Outcomes in Women after the Fontan Procedure The consensus is that pregnancy is possible and often tolerated, but it carries substantially higher risks than in the general population and demands close collaboration between cardiologists and obstetricians throughout.
Medications That Help
Because the Fontan depends so heavily on low pulmonary resistance, drugs that relax the lung blood vessels have been a natural target. A meta-analysis of randomized trials found that pulmonary vasodilators significantly improved functional class, increased six-minute walking distance by about 134 meters, and modestly improved peak oxygen consumption. They also lowered mean pulmonary artery pressure. Side effects were generally mild.32PubMed Central. The efficacy and safety of pulmonary vasodilators in patients with Fontan circulation: a meta-analysis of randomized controlled trials These drugs do not appear to reduce mortality, but for patients whose daily functioning is limited, the improvements in how far they can walk and how they feel can be meaningful.
When the Fontan Fails
The Fontan circulation is inherently progressive in its decline. When it fails, options narrow to mechanical heart support or transplantation. Ventricular assist devices have been used in Fontan patients with impaired heart muscle function, but they are less helpful when the dominant problem is lymphatic dysfunction rather than a weak ventricle.33JHLT Open. Mechanical circulatory support in failing single-ventricle physiology
Heart transplantation remains the definitive treatment for Fontan failure, but the near-universal presence of liver disease complicates the picture. When significant liver damage coexists with heart failure, combined heart-liver transplantation may offer better long-term results. One study found that in patients with substantial liver disease, combined transplant was associated with better five-year survival compared with heart transplant alone (about 77% versus 42%).34PubMed. Clinical Outcomes of Adult Fontan-Associated Liver Disease and Combined Heart-Liver Transplantation A more recent meta-analysis, however, found that the survival advantage of combined transplant was less clear when only modern-era transplants were analyzed.35PubMed Central. Mortality Outcomes of Combined Heart and Liver Transplantation and Isolated Heart Transplantation Following Fontan Procedures: A Systematic Review and Meta-Analysis Regardless of strategy, transplantation in Fontan patients is complex and carries high rates of perioperative complications, but it remains a reasonable option for those with end-stage failure.36PubMed. Heart and heart-liver transplantation in adults with failing Fontan physiology
Quality of Life and the Psychological Dimension
Across all age groups, people living with a Fontan circulation report lower health-related quality of life than the general population.37PubMed Central. Health-Related Quality of Life in Children, Adolescents, and Adults With a Fontan Circulation: A Meta-Analysis Yet the picture is more nuanced than that summary suggests. In one Australian and New Zealand registry study of adults (average age about 30), the majority rated their overall quality of life at 6 or higher out of 10, despite scoring lower than population norms on physical and social functioning. The strongest predictors of lower quality of life were not medical variables but psychological ones: general stress, medical traumatic stress, communication difficulties, and lack of emotional support. Together, psychological and relational factors explained far more of the variation in quality of life than clinical characteristics did.38PubMed Central. Quality of Life and Well-Being in Adults With Fontan Physiology: Findings From the Australian and New Zealand Fontan Registry Quality of Life Study This finding has practical implications: investing in mental health screening and support services may matter as much as optimizing medications.
The Cost of a Lifetime of Care
The financial burden is substantial. From birth through age 18, the average hospital inpatient cost for a Fontan patient in the United States was estimated at roughly $390,000 (in 2014 dollars), with about 164 inpatient days. A striking detail is that over 40% of those pediatric hospital costs accumulated after the final planned surgery, reflecting the ongoing need for management of complications.39PubMed. Hospital Inpatient Costs for Single Ventricle Patients Surviving the Fontan Procedure
Access to specialized care is another concern. A study found that only about a third of adult Fontan patients had visited an adult congenital cardiologist within a two-year period, and a similar fraction had seen any adult cardiologist at all.40The Journal of Thoracic and Cardiovascular Surgery. Resolving the Fontan paradox: Addressing socioeconomic and racial disparities in patients with a single ventricle Given the severity of the underlying condition and the number of organ systems involved, that level of surveillance is concerning. The transition from pediatric to adult cardiology care remains a vulnerable gap, and socioeconomic disparities compound the problem. Patients who lose contact with specialized care are the ones most likely to present later with advanced, harder-to-treat complications.