--- title: Hypoplastic left heart syndrome description: What hypoplastic left heart syndrome is, why the life of a newborn with this defect depends on the open ductus arteriosus, how it is found, how the staged operations work and when urgent help is needed. type: disease aliases: - HLHS - Hypoplastic left heart - Left heart hypoplasia sources: - tier: guideline org: minzdrav-rf title: Синдром гипоплазии левых отделов сердца year: 2024 url: https://cr.minzdrav.gov.ru/view-cr/602_2 - 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: Hypoplastic Left Heart Syndrome year: 2023 url: https://www.msdmanuals.com/professional/pediatrics/congenital-cardiovascular-anomalies/hypoplastic-left-heart-syndrome sources_checked: 2026-10-13 review: null --- Hypoplastic left heart syndrome (HLHS) is a congenital heart defect in which the structures of the left side of the heart are underdeveloped. The mitral and/or aortic valves are affected, most often closed off completely (atresia), and, following from this, the left ventricle, the ascending aorta and the aortic arch are underdeveloped. After birth, the left side of such a heart cannot pump enough blood to the body. The right ventricle takes over this work, but its blood reaches the body only through the [open ductus arteriosus](../patent-ductus-arteriosus/), a vessel that connects the pulmonary artery to the aorta and closes on its own after birth. When the duct closes, the circulation quickly fails. Without surgery, almost all children with this defect die by 6 months of age.

Normally, oxygen-rich blood from the lungs enters the left atrium and passes through the mitral valve, the left ventricle and the aortic valve into the aorta. The right ventricle sends blood along the pulmonary artery to the lungs, and the ductus arteriosus closes after birth.

The diagram shows the most severe form of the defect, in which the mitral and aortic valves are closed off completely (atresia). The left ventricle is small, and the ascending aorta and the aortic arch are narrow. Blood from the lungs leaves the left atrium through an opening between the atria into the right side of the heart and mixes there with venous blood. The right ventricle pumps the mixed blood into the pulmonary artery, and it reaches the body only through the open ductus arteriosus. Blood flows backwards from the duct into the arch and the ascending aorta.

## Why it happens The defect forms at an early stage of fetal development. Why it happens is not fully understood. The most likely cause is damage to the aortic and mitral valves. The ascending aorta and the arch stay narrow because little or no blood reaches them through the diseased valve. In some children genetic factors play a part in the defect, but they are complex and poorly understood. The defect is rare: according to the Russian Ministry of Health guideline, it occurs in 0.16–0.2 per 1,000 live births, twice as often in boys as in girls. Left heart lesions form a spectrum: from isolated ones, such as [coarctation of the aorta](../coarctation-of-the-aorta/), to multilevel ones, a combination of aortic and mitral atresia with a rudimentary left ventricle. There is no generally accepted classification of HLHS; a division by valve morphology is used: stenosis or atresia of the aortic and mitral valves in various combinations, and hypoplastic left heart complex. The most severe form is atresia of both valves: there is no antegrade flow in the ascending aorta, and systemic haemodynamics is possible only with a patent ductus arteriosus (PDA) and an interatrial communication; the right ventricle sustains the systemic circulation through retrograde flow in the aortic arch via the PDA. The prognosis is considerably worse with tricuspid and pulmonary valve involvement, a restrictive interatrial communication or an intact atrial septum. Genetic syndromes are present in ~10–25% of patients: most often Turner, Noonan and Holt–Oram syndromes, trisomies, CHARGE association and Jacobsen syndrome. HLHS is the most common defect with single-ventricle physiology. According to the Russian Ministry of Health guideline, it accounts for 1.4% to 9% of all congenital heart defects; according to MSD Manuals, for 2–4%. ## Symptoms Right after birth, a baby may look almost healthy: while the ductus arteriosus is wide, blood reaches the organs. Symptoms appear when the duct begins to close. According to MSD Manuals, this usually happens during the first 24 to 48 hours of life; the Russian Ministry of Health guideline says that signs of the disease appear in the first few hours of life or at 2–3 days of age. The baby starts breathing fast and hard, the heart rate rises, and the pulse in the arms and legs becomes weak. The skin is pale, grey or bluish, and the hands and feet are cold. The baby is floppy, feeds poorly and passes little urine. Without help, shock quickly develops: a severe, life-threatening failure of the circulation. If the opening between the atria is narrow or absent, blood backs up in the lungs. This is a critical situation from the first hours of life, and an emergency procedure is needed to widen this opening. Immediately after birth, while pulmonary vascular resistance is relatively high and the PDA is wide, physical findings are most often close to normal. As pulmonary resistance falls naturally, more blood goes to the pulmonary circulation at the expense of systemic flow: tachypnoea, relative hypotension and acidosis appear; when the PDA closes, systemic perfusion deteriorates further. Typical findings are tachycardia, dyspnoea, acrocyanosis or cyanosis that increases with agitation, hepatomegaly and low blood pressure; there is no direct correlation between the severity of the condition and the degree of cyanosis. On auscultation there is a moderate systolic murmur at the left sternal border from the functioning PDA, and the second heart sound over the aorta is single. Without treatment, cardiogenic shock with metabolic acidosis and oliguria or anuria rapidly develops. ## How it is diagnosed The defect is often found before birth. According to the Russian Ministry of Health guideline, an ultrasound of the fetal heart can raise suspicion of it at 16–18 weeks of pregnancy. According to MSD Manuals, most children are now diagnosed before birth. If the defect is known in advance, delivery is recommended in a hospital with a neonatal intensive care unit, close to a cardiac surgery centre. After birth, the main test is an ultrasound of the heart (echocardiography): it confirms the diagnosis and helps choose the operation. A chest X-ray and an ECG are also done, and if the ultrasound does not give enough information, a CT or MRI scan of the heart. Transthoracic echocardiography with colour Doppler mapping is recommended for all patients with suspected HLHS (level of evidence 4, grade of recommendation C). It assesses the valves, the ascending aorta and the arch, antegrade flow, the size of the left ventricle, the interatrial communication and the PDA, and right ventricular and tricuspid valve function. Cardiac catheterisation and panaortography are not recommended in newborns with HLHS (level of evidence 5, grade of recommendation C). The chest X-ray shows cardiomegaly due to the right heart chambers and pulmonary plethora; ECG changes are nonspecific, with signs of right heart overload. Metabolic acidosis that worsens when supplemental oxygen is administered is characteristic of HLHS: oxygen lowers pulmonary vascular resistance, so more of the right ventricular output flows to the lungs rather than through the PDA to the systemic circulation. ## How it is treated This defect is always critical: once the diagnosis is confirmed, the baby is moved straight to intensive care and as quickly as possible to a cardiac surgery hospital. A medicine from the prostaglandin group is given into a vein to keep the ductus arteriosus from closing. Extra oxygen can do harm with this defect: it widens the blood vessels of the lungs, so more blood goes to the lungs and less to the body. Whether oxygen is needed, and how much, is decided by the doctor. The defect cannot be fully corrected. Treatment is a series of operations, one after another. Their aim is for the single working ventricle, the right one, to pump blood to the body, while blood reaches the lungs by another route. These operations do not make the heart normal: they only create acceptable conditions for the child to live and develop. - **Norwood operation**, in the first week of life. From the pulmonary artery and the small aorta, the surgeon builds a new aorta that arises from the right ventricle. The ductus arteriosus is tied off, blood is sent to the lungs through a small tube (a shunt), and the opening between the atria is widened. - **Hybrid first stage**, instead of the Norwood operation at the start of treatment. A stent is placed in the ductus arteriosus so that blood keeps flowing to the body, and narrowing bands are placed on both branches of the pulmonary artery so that not too much blood goes to the lungs. The Norwood operation is then done later, as the second stage. According to the Russian Ministry of Health guideline, this route is chosen, for example, when the baby is extremely ill or has a low body weight. - **Glenn operation** (bidirectional cavopulmonary anastomosis). The superior vena cava is joined directly to the pulmonary artery, and about half of the venous blood goes to the lungs, bypassing the heart. According to MSD Manuals, it is done at 3 to 6 months of age; the Russian Ministry of Health guideline gives an age of 2–10 months and stresses that the timing is different for each child. - **Fontan operation**, at 1.5–3 years, the final stage. Blood from the inferior vena cava is also sent directly into the pulmonary artery; the Russian Ministry of Health guideline advises doing this through a tube (conduit) outside the heart. After this, venous blood flows to the lungs without the help of a ventricle, the ventricle pumps blood only to the body, and arterial and venous blood hardly mix. The circulation after the Fontan operation is not the same as in a healthy heart: the pressure in the veins is constantly raised, and complications may develop over the years. Additional procedures are often needed between and after the stages, for example if the tricuspid valve starts to leak or the reconstructed aorta narrows. If the right ventricle or the tricuspid valve works poorly, the only alternative to staged operations is a heart transplant, but donor hearts are very scarce. Treatment is carried out in centres with wide experience of these operations. After each stage, the child is followed up by a paediatric cardiologist experienced with congenital heart defects, and also by a neurologist. Parents are taught to watch at home the child's breathing during sleep, how much the child eats and the child's weight, and to report any changes to the doctor. Adults after the Fontan operation are followed up in specialised centres, usually at least once a year. The Russian Ministry of Health guideline: staged surgical treatment creating single-ventricle physiology in three stages, the Norwood operation, the bidirectional cavopulmonary anastomosis (BCPA, Glenn) and the Fontan operation (level of evidence 4, grade of recommendation C). The first stage is Norwood–Sano or Norwood–Blalock within the first week of life; BCPA at 2–10 months; Fontan at 18–36 months, as an extracardiac conduit modification (all level of evidence 4, grade of recommendation C). Pulmonary blood flow in the Norwood procedure is provided by a modified Blalock–Taussig–Thomas shunt or a right ventricle–pulmonary artery conduit (Sano modification). A hybrid stage I (bilateral pulmonary artery banding and PDA stenting) is recommended for extremely severe illness, admission after 1 week of life or low body weight (level of evidence 4, grade of recommendation C); the second stage is then Norwood–BCPA, or Norwood–Sano or Norwood–Blalock at 3–5 months. The Fontan operation consists of the separation of the systemic and pulmonary venous returns without a subpulmonary ventricle and restores them to being "in series". In patients with particular anatomy or hypoplastic left heart complex, operations aimed at preserving biventricular physiology are recommended; such repair is possible only in certain cases and is often risky. After the Fontan operation, the lack of a subpulmonary ventricle results in chronic systemic venous hypertension, altered pulmonary haemodynamics and a chronically "preload-deprived" ventricle. Late problems include declining systemic ventricular function, atrioventricular valve regurgitation, liver disease ranging from congestion to severe fibrosis and, rarely, protein-losing enteropathy. Adults with HLHS remain a small but expanding group; early data in adulthood suggest that they are more prone to complications than other Fontan patients, warranting closer follow-up. It is recommended that women with a Fontan circulation and any complication are counselled against pregnancy (ESC). The mortality risk for children with HLHS is highest in the first year of life; survivors may have neurodevelopmental disability. ## When to call an ambulance HLHS is a critical defect: a newborn's condition can suddenly get worse at any moment, and closure of the ductus arteriosus leads to rapid failure of the circulation. The defect is often found before birth, but if a newborn is breathing fast and hard, has pale, grey or bluish skin, has cold hands and feet, has become floppy, feeds poorly or passes little urine, call your local emergency number (112 in the EU, 911 in the US and Canada, 999 in the UK). Between operations the general safety rule applies: for severe shortness of breath or fainting, call your local emergency number (112 in the EU, 911 in the US and Canada, 999 in the UK). Report changes in breathing during sleep, appetite and weight to the child's doctor. 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). New swelling, a marked drop in exercise tolerance, new-onset irregular heartbeat, blueness or coughing up blood are reasons not to put off seeing your cardiologist.