--- title: Single ventricle description: What a functionally single ventricle is, which heart defects belong to this group, why the staged Glenn and Fontan operations are needed, why they do not cure the defect, how people live after the Fontan operation and when urgent help is needed. type: disease aliases: - UVH - Functionally single ventricle - Univentricular heart - Single ventricle heart - Common ventricle - Three-chambered heart - Double-inlet left ventricle - Tricuspid atresia - Fontan circulation sources: - tier: guideline org: minzdrav-rf title: Единственный желудочек сердца year: 2025 url: https://cr.minzdrav.gov.ru/view-cr/44_3 - tier: guideline org: esc title: 2020 ESC Guidelines for the management of adult congenital heart disease year: 2020 doi: 10.1093/eurheartj/ehaa554 url: https://doi.org/10.1093/eurheartj/ehaa554 - tier: reference org: msd-manuals title: Other Congenital Cardiac Anomalies year: 2023 url: https://www.msdmanuals.com/professional/pediatrics/congenital-cardiovascular-anomalies/other-congenital-cardiac-anomalies - tier: reference org: msd-manuals title: Tricuspid Atresia year: 2023 url: https://www.msdmanuals.com/professional/pediatrics/congenital-cardiovascular-anomalies/tricuspid-atresia sources_checked: 2026-10-13 review: null --- Single ventricle is a congenital heart defect in which both atria are connected to only one well-developed ventricle. The second ventricle is absent or so underdeveloped that the heart cannot be made normal, with two fully working ventricles. That is why doctors speak of a functionally single ventricle: it is not one defect but a group of defects in which only one ventricle works. In a healthy heart, blood passes through the lungs and through the body in turn. In single ventricle, the pulmonary and systemic circulations work in parallel rather than in series. Blood from the lungs and blood from the body mix in one chamber, so the blood carries less oxygen than normal. The defect is rare: according to the Russian Ministry of Health guideline, it occurs in about 0.13 per 1,000 newborns, which is 2.5% of all congenital heart defects. Without surgery the outlook is poor. Treatment is a series of operations, one after another. They do not create a second ventricle: these operations are palliative, which means they do not cure the defect but ease the condition by improving the circulation in a heart with a complex structure.

Normally the heart has four chambers, and blood passes through the lungs and through the body in turn: the pulmonary and systemic circulations work in series.

The diagram shows one of several variants of the defect, double-inlet left ventricle with transposition of the great arteries; according to the Russian Ministry of Health guideline, it is the most common one. Both atria open into one large ventricle, while the second, underdeveloped one remains a small outlet chamber joined to the main one by an opening. Blood from the lungs and from the body mixes in the common ventricle. The aorta and the pulmonary artery can arise either from the main ventricle or from the outlet chamber; here the pulmonary artery arises from the main one and the aorta from the outlet chamber.

## Why it happens The defect forms before birth: most often, the development of one or both ventricles of the fetal heart is delayed. The predisposing factors are the same as for other congenital heart defects. Several different defects count as a single ventricle: - double-inlet left or right ventricle: both atria open into one ventricle; - tricuspid or mitral atresia: one of the valves between an atrium and a ventricle is missing; - unbalanced atrioventricular canal: a common valve and only one fully developed ventricle; - [hypoplastic left heart syndrome](../hypoplastic-left-heart-syndrome/), which has its own article; - rare forms that do not fit these groups. How the disease runs depends largely on how much blood goes to the lungs. If nothing narrows the way to the lungs, too much blood flows there, and [heart failure](../heart-failure/) and [pulmonary hypertension](../pulmonary-hypertension/) (damage to the blood vessels of the lungs) develop. If the pulmonary artery is narrowed, lack of oxygen comes to the fore. The single ventricle works under a double load, and over time this leads to thickening of its walls and to heart failure. The most common variant is double-inlet LV with [transposition of the great arteries](../transposition-of-the-great-arteries/). If the aorta arises from the outlet chamber, the route from the systemic ventricle to the aorta passes through the bulboventricular foramen, which is in effect a VSD. Over time it may narrow (subaortic stenosis) and obstruct systemic flow. Long-standing excessive pulmonary blood flow leads to sclerotic changes in the pulmonary vessels and to pulmonary hypertension. The [patent ductus arteriosus](../patent-ductus-arteriosus/) may play an important role (duct-dependent conditions). The 3D model shows a normal heart: highlighted are both ventricles, the interventricular septum and the tricuspid valve. In single ventricle, the second ventricle and the septum are underdeveloped or absent, and in tricuspid atresia the tricuspid valve is missing too. ## Symptoms If too little blood reaches the lungs, blueness of the skin (cyanosis) appears at birth or soon after. It gets worse with crying, feeding and movement. If too much blood goes to the lungs, there may be almost no blueness, but signs of heart failure appear: fast, laboured breathing, especially during feeding or active play, sweating, the child copes less well with usual activity, and the abdomen gets bigger. Most patients are short of breath. Because of the constant lack of oxygen, the fingertips gradually become thicker, like "drumsticks" (clubbing). Many children lag behind in physical development. If the route for blood into the aorta is narrowed as well, shock, a life-threatening failure of the circulation, can develop quickly. The clinical picture is determined by volume overload of the heart and pulmonary hypertension in patients without PA stenosis, and by marked hypoxaemia in patients with PA stenosis. With excessive pulmonary blood flow, dyspnoea is combined with signs of HF, ranging from sweating and tachycardia to hepatomegaly, oedema, ascites and/or hydrothorax. With associated subaortic stenosis, arch hypoplasia or coarctation of the aorta, hypoperfusion progresses rapidly, up to shock; patients with combined obstruction of systemic and pulmonary flow are, as a rule, not viable. Adults without a Fontan operation are usually cyanotic, and exercise capacity is, as a rule, markedly reduced. Complete AV block, supraventricular and ventricular arrhythmias (sudden cardiac death is not unusual), stroke, brain abscess and thromboembolism may occur; endocarditis is relatively common in this group. ## How it is diagnosed The defect may be found before birth on a fetal ultrasound scan. If not, after birth the diagnosis is made with an ultrasound of the heart (echocardiography). The Russian Ministry of Health guideline calls it the leading method that establishes the final diagnosis. The oxygen level in the blood is also measured (pulse oximetry), and an ECG and a chest X-ray are done. Before operations, a CT or MRI scan of the heart and cardiac catheterisation, a test done through a thin tube passed along a blood vessel, may be needed. Echocardiography (grade of recommendation C, level of evidence 5) shows the absence of the interventricular septum, AV valves opening into the single ventricle, the outlet chamber and the great artery arising from it. Contrast-enhanced cardiac CT is recommended for critically ill patients before surgery, and MRI for choosing the approach and timing of surgery and for routine assessment after it. Angiocardiography is performed when needed, including to assess the size of the pulmonary arteries, pulmonary vascular resistance and additional sources of pulmonary blood flow. ## How it is treated Treatment comes in several stages. Which operations are needed depends above all on the blood flow to the lungs. Newborns with very little blood flow to the lungs are given, in hospital, a medicine from the prostaglandin group to keep the ductus arteriosus open. The first operation may be: - narrowing the pulmonary artery with a band (pulmonary artery banding, the Muller operation) if too much blood goes to the lungs: this protects the blood vessels of the lungs; - a systemic-to-pulmonary shunt, a connection between an artery and the pulmonary artery, if too little blood goes to the lungs; - widening a too-narrow opening between the atria with a balloon (balloon atrial septostomy, the Rashkind procedure). The Norwood operation, the first stage in hypoplastic left heart syndrome, is described in a [separate article](../hypoplastic-left-heart-syndrome/). Next, all venous blood is sent to the lungs, bypassing the heart. This used to be done in one operation, but mortality was high, so the operation was split into two stages. - **Glenn operation** (bidirectional cavopulmonary anastomosis). The superior vena cava is joined to the pulmonary artery, and blood from the upper half of the body goes straight to both lungs, bypassing the heart. This unloads the ventricle and reduces blueness. According to the Russian Ministry of Health guideline, it is preferably done in the first year of life, but not before 4 months of age. - **Fontan operation**, the final stage. Blood from the inferior vena cava is also sent into the pulmonary artery: most often through a synthetic tube (conduit) outside the heart, sometimes through a tunnel inside the atrium; the surgeon chooses the method. According to the Russian Ministry of Health guideline, it is done not before 2 years of age. After it, all venous blood goes to the lungs, the single ventricle pumps blood only to the body, the blood streams no longer mix, and the child "turns pink". To lower the risk, the surgeon often leaves a small "window" (fenestration) between the Fontan pathway and the atrium. The Fontan operation is not done for everyone: it needs low pressure in the blood vessels of the lungs, good ventricular function and pulmonary arteries of adequate size. The Russian Ministry of Health guideline advises against it with sclerotic changes in the blood vessels of the lungs, marked ventricular weakness or congestive liver damage, and recommends a heart transplant for severe ventricular weakness. For heart failure, diuretic medicines are used. After the Glenn and Fontan operations, blood flows more slowly in the veins, and the risk of clots is higher. The Russian Ministry of Health guideline advises lifelong prevention of blood clots after these operations. The ESC guideline says that for adults after the Fontan operation the benefit of routine prevention for everyone has not been proven and that centres differ in practice. According to the ESC, anticoagulants are needed if there is now, or has been, a clot in the atrium, an atrial arrhythmia or thromboembolism. Whether medicines are needed, which ones and how to monitor them is decided only by the treating doctor. After each stage, rehabilitation for at least 6 weeks is needed, most often at home. For the first 3 months the arms and shoulders must not be put under heavy strain, and fluid intake is limited; the doctor will say by how much. Haemodynamic correction is a total cavopulmonary connection (a "complete bypass" of the right heart) to reduce systemic ventricular preload and improve oxygenation. First, BCPA, an end-to-side anastomosis between the SVC and a PA branch (alternative: hemi-Fontan), then an IVC–PA anastomosis (both grade of recommendation C, level of evidence 5). Age criteria: BCPA not before 4 months, Fontan not before 2 years (grade of recommendation C, level of evidence 4). When the risk of the Fontan operation is high, palliative procedures are possible as the "final" stage or as a "bridge" to transplantation (grade of recommendation C, level of evidence 5); heart transplantation is recommended for severe systemic ventricular dysfunction (grade of recommendation C, level of evidence 4). ## Life after the Fontan operation The circulation after the Fontan operation is not the same as in a healthy heart. There is no ventricle to pump blood to the lungs, the pressure in the veins is constantly raised, and the single ventricle does not receive enough blood. Most children after the Fontan operation do well in childhood and adolescence, although their stamina is reduced. But over the years heart function inevitably declines earlier than in healthy people, even after the best result of surgery. Late complications named by both the Russian Ministry of Health guideline and the ESC guideline: - congestion from high pressure in the veins: an enlarged liver, fluid in the abdomen and around the lungs, swelling, blueness; - heart rhythm disorders, often atrial ones, for example [atrial flutter](../atrial-flutter/); - liver damage, from congestion to severe fibrosis and cirrhosis, and liver cancer is possible, so the liver is checked regularly; - protein-losing enteropathy, a rare but serious complication that causes swelling and fluid in the abdomen and around the lungs; - blood clots and thromboembolism. Sometimes further procedures are needed, on the pulmonary arteries, a valve or the tube (conduit) once the child has "outgrown" it. If the Fontan circulation starts to fail, a repeat operation or a heart transplant is considered. **Follow-up is lifelong.** According to the Russian Ministry of Health guideline, the local cardiologist is seen at least every 6 months, and a check-up at a specialised centre is done at least every 6–12 months. An ultrasound of the heart is done in the first month after discharge, then at least every 6–12 months, and after the Fontan operation liver function tests are checked just as often. The ESC recommends that adults after the Fontan operation are followed up at a specialised adult congenital heart disease centre, usually at least once a year, with an ultrasound of the heart, an ECG, blood tests and an exercise test. **Exercise.** The level of physical activity is chosen individually. For adults after the Fontan operation, the ESC recommends moderate aerobic exercise within the limits of how they feel. **Pregnancy.** Before planning a pregnancy, women after the Fontan operation need a full assessment that must include an ultrasound of the heart. The ESC recommends that women with a Fontan circulation and any complication do not plan a pregnancy. **Endocarditis prevention.** Here the guidelines differ. The Russian Ministry of Health guideline says that antibiotic cover to prevent [infective endocarditis](../infective-endocarditis/) is mandatory for any procedure that risks damaging the skin or mucous membranes, at the dentist, the beautician and elsewhere, and that such procedures should be agreed with the cardiologist in advance. The ESC considers prevention indicated for all adults with a single ventricle who have not had a Fontan operation, and after the Fontan operation only after a redo Fontan operation in the last 6 months, with cyanosis, a prosthetic valve, a residual leak at a patch or previous endocarditis. Whether prevention is needed before a particular procedure is decided by the cardiologist. The absence of a subpulmonary ventricle results in chronic systemic venous hypertension, altered pulmonary haemodynamics and a chronically "preload-deprived" ventricle. Protein-losing enteropathy presents with hypoalbuminaemia, oedema, ascites, pleural effusion or chylothorax, immunodeficiency and hypocalcaemia; immediate hospital admission is recommended when it is suspected (grade of recommendation C, level of evidence 3). In a "failing Fontan", surgery is considered; with systemic ventricular failure, heart transplantation in an experienced centre may help. ## When to call an ambulance In a newborn with this defect the condition can get worse quickly: if the route for blood into the aorta is narrowed, shock can develop. The Russian Ministry of Health guideline lists the reasons for emergency admission to hospital: heart failure getting worse over recent weeks or days, a fall in the blood oxygen level over the same period, and suspected protein-losing enteropathy. If tiredness, breathlessness, blueness or swelling appears or suddenly gets worse, the abdomen gets bigger, an irregular heartbeat appears, or there is a fever without a clear cause, the Russian Ministry of Health guideline advises an unscheduled visit to the cardiologist as soon as possible. If the condition is severe (the person is breathless at rest, the lips and skin have suddenly turned very blue, or the baby is floppy or cannot feed), do not wait for an appointment: call your local emergency number (112 in the EU, 911 in the US and Canada, 999 in the UK). Do the same straight away for fainting or signs of a stroke (sudden weakness or numbness of an arm or leg, trouble speaking or seeing, even if brief). In adults after the Fontan operation, a prolonged episode of fast heartbeat is an emergency: call your local emergency number (112 in the EU, 911 in the US and Canada, 999 in the UK).