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Dr. Alessandro Giardini
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The Fontan operation is the third and final stage of surgical palliation for hypoplastic left heart syndrome. It is performed at around two to four years of age, when the child has grown sufficiently and the pulmonary circulation has demonstrated it can accommodate the increased passive venous return that the Fontan arrangement requires.
The Fontan is the endpoint of the staged palliation that began with the Norwood procedure in the first week of life. Completing it marks a significant milestone for families. Understanding what the operation does, what the resulting circulation means for the child's body over time, and what follow-up involves is essential preparation for the years ahead.
The Glenn procedure, performed at stage two, connected the superior vena cava directly to the pulmonary arteries, allowing the blood returning from the upper body to flow passively to the lungs. The Fontan operation completes this process by connecting the inferior vena cava, which drains deoxygenated blood from the lower body and abdominal organs, to the pulmonary circulation as well.
After the Fontan, all systemic venous blood flows directly and passively to the lungs, driven by the pressure gradient between the systemic veins and the pulmonary circulation, without passing through a pumping chamber. The single right ventricle now receives only oxygenated blood returning from the lungs and pumps it out to the body. The circulations are separated.
This is described as a total cavopulmonary connection. It is not a normal circulation. No pumping chamber drives blood to the lungs. The Fontan circulation relies on passive flow, which means pulmonary vascular resistance must remain low, and the single ventricle must maintain adequate systemic output to generate the driving pressure for passive pulmonary flow. These physiological constraints define the vulnerabilities of the Fontan circulation for life.
Two surgical variants are in current use, and families will hear both discussed.
The extracardiac Fontan uses a synthetic tube, typically a Gore-Tex conduit, to connect the inferior vena cava to the pulmonary arteries outside the heart substance itself. This avoids the need to open the atria, reduces the risk of atrial arrhythmia, and produces a smooth-walled, low-turbulence flow path. This is the modification used by the surgical teams at Great Ormond Street Hospital and the Portland Hospital in London.
The lateral tunnel Fontan creates the connection by constructing a tunnel along the inside wall of the right atrium using a patch, directing inferior vena cava blood through the atrial chamber to the pulmonary arteries. This approach uses the child's own tissue rather than synthetic material for part of the circuit, which may have theoretical growth advantages in younger children.
Most centres today prefer the extracardiac technique, which is associated with lower early arrhythmia rates. Both produce equivalent Fontan physiology, and the choice depends on the individual anatomy and the surgical team's experience.
Many Fontan operations include a deliberate small communication between the Fontan circuit and the right atrium, known as a fenestration. The purpose is to provide a pop-off valve: if venous pressure rises acutely in the early postoperative period, blood can flow through the fenestration into the atrium and then the ventricle, reducing the venous backpressure at the cost of some mixing of deoxygenated blood and a corresponding drop in saturations.
Fenestrations are associated with better early haemodynamics, shorter intensive care stays, lower rates of pleural effusions, and faster hospital discharge in the early postoperative period. The trade-off is permanent mild cyanosis from the ongoing right-to-left shunt through the fenestration, and a small but real risk of paradoxical embolism. Some fenestrations are subsequently closed by cardiac catheter once the Fontan circulation has stabilised, typically six to twelve months after the operation.
Whether to include a fenestration and when to close it are decisions made by the surgical and cardiology team based on the individual child's haemodynamics and anatomy.
The Fontan is a major cardiac operation under cardiopulmonary bypass, and recovery takes several weeks. The intensive care stay is typically three to five days. The most consistent postoperative challenge is the development of pleural effusions, which occur for the same reason as after the Glenn procedure: elevated systemic venous pressure increases lymphatic flow, which can transiently exceed absorptive capacity. Effusions are managed with chest drains and dietary fat restriction, and they usually resolve within two to three weeks.
Most children are in hospital for two to four weeks in total. On discharge, families are given guidance on activity restriction, wound care, medications, and follow-up. A cardiologist review with echocardiogram is performed four to six weeks after discharge to assess how the Fontan circulation is functioning.
Children who recover well from the Fontan procedure often experience a remarkable period of improvement in the months that follow. For the first time, the circulation is fully separated and the right ventricle is no longer working against a mixed volume load. Energy improves, growth improves, and many children make significant developmental progress.
Oxygen saturations after a completed Fontan run in the 92 to 96% range, substantially higher than at any previous stage. Exercise capacity remains below that of healthy peers but is meaningfully better than after the Glenn.
Medications after the Fontan typically include aspirin or anticoagulation to reduce the risk of thrombus formation within the low-flow Fontan circuit, and some children remain on diuretics or ACE inhibitors depending on ventricular function. The specific medication regimen is tailored to the individual child and reviewed regularly.
School attendance, peer relationships, and developmental progression are the normal goals of this period. Neurodevelopmental follow-up continues, and educational support is arranged where needed. Physical activity is encouraged within the limits of the Fontan physiology: moderate regular exercise is actively beneficial, while high-intensity competitive sport is generally advised against.
The Fontan circulation is ingenious but it is not sustainable without consequence over decades. The physiological abnormalities that define it, specifically elevated systemic venous pressure and passive rather than active pulmonary perfusion, have long-term effects on multiple organ systems that families need to understand as their child grows.
These long-term complications are covered in detail in the dedicated post on long-term outlook and Fontan complications. They include Fontan-associated liver disease, arrhythmias, protein-losing enteropathy, plastic bronchitis, declining exercise capacity, and eventually Fontan failure requiring cardiac transplantation in a proportion of patients. Regular, lifelong specialist follow-up is the mechanism by which these complications are identified and managed before they become irreversible.
Transition from paediatric to adult congenital heart disease care in the mid-teens is a planned and important step, not an administrative handover. Ensuring continuity of care with an adult congenital heart specialist who understands the Fontan physiology is one of the most important things families can do as the child approaches adulthood.
Most children have the Fontan between the ages of two and four years. The exact timing is determined by the child's size, the pulmonary artery anatomy and pressures confirmed at the time of measurement, and right ventricular function. Most children benefit from waiting until age three or four. The timing decision is made collaboratively by the surgical and cardiology team.
Most children are placed on anticoagulation or antiplatelet therapy after the Fontan procedure to reduce the risk of clot formation within the low-flow circuit. The choice between aspirin and full anticoagulation with warfarin or a newer oral anticoagulant depends on the anatomy, the presence of a fenestration, and individual risk factors. The regimen is reviewed regularly and may change over time.
Cardiac catheterisation is sometimes performed at defined intervals during long-term Fontan follow-up, but most recently cardiac MRI has developed as an alrternative for surveillance over cardiac catheterization. The timing of the first post-Fontan catheterisation and subsequent ones is determined by the follow-up team based on the individual clinical picture.
Many children do. Attending school, building friendships, pursuing hobbies, and participating in everyday activities are all achievable goals after the Fontan. There will be physical activity limitations and the need for ongoing medical management, but these do not prevent a childhood that is rich, connected, and meaningful. Quality of life data from adolescents with a Fontan circulation show self-reported wellbeing scores that, for many, are comparable to those of healthy peers.
Author: Dr. Alessandro Giardini, MD, PhD, Consultant Paediatric Cardiologist
Written 22/06/2026