Hypoplastic left heart syndrome !

A baby is born with a tiny left heart that cannot pump to the body. It needs urgent care and several surgeries in the first years.

Updated 2026-11-01

Structures involved

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Why it happens

What it is

Hypoplastic left heart syndrome (HLHS) is a critical congenital heart defect in which the left-sided structures are severely underdeveloped: mitral stenosis or atresia, a small left ventricle, aortic stenosis or atresia and a hypoplastic ascending aorta and arch, often with coarctation. The right ventricle must supply both the lungs and, through the ductus arteriosus, the body, so systemic circulation is ductus-dependent.

Who gets it

About 2–3% of congenital heart disease, roughly 1 in 4,000 live births, more frequent in boys. It is one of the leading causes of death from heart disease in the first week of life. In Colombia and Latin America, outcomes depend heavily on prenatal diagnosis and timely transfer to the few centres that offer staged neonatal surgery.

Causes

Abnormal development of the left heart in early pregnancy; the exact cause is unknown in most cases
Reduced flow through the left heart in fetal life (for example premature restriction of the foramen ovale or fetal aortic stenosis) leads to under-growth
Genetic associations: Turner syndrome, Jacobsen syndrome (11q deletion), trisomies 13 and 18, familial left-sided obstructive lesions

Risk factors

Family history of left-sided obstructive heart defects (bicuspid aortic valve, coarctation)
Chromosomal abnormalities
Male sex

Pathophysiology

Oxygenated pulmonary venous blood cannot leave the small left heart and must cross the atrial septum to the right atrium, where it mixes with systemic venous return. The right ventricle pumps the mixed blood into the pulmonary trunk; part goes to the lungs and part reaches the aorta through the ductus arteriosus, filling the ascending aorta and coronary arteries retrogradely. When the ductus closes in the first days, systemic perfusion collapses, with shock and metabolic acidosis. A restrictive atrial septum causes severe pulmonary venous congestion and hypoxaemia at birth. Balance between pulmonary and systemic flow is delicate: falling pulmonary resistance (for example with high inspired oxygen) steals flow from the body.

Classification

Anatomical subtypes by valve status: mitral and aortic atresia (most severe), mitral stenosis with aortic atresia, mitral and aortic stenosis
With intact or highly restrictive atrial septum (high-risk subgroup)

Symptoms and signs

Often well at birth, then deterioration in the first days as the ductus closes
Tachypnoea, poor feeding and lethargy
Grey or pale colour, cool extremities, weak or absent pulses in all limbs
Mild cyanosis
Shock with oliguria and metabolic acidosis

Diagnosis

Clinical: Many cases are diagnosed prenatally on the four-chamber view of the fetal ultrasound, confirmed by fetal echocardiography. After birth: a newborn in shock with diffusely weak pulses, single loud S2 and often no significant murmur.
Tests: Pulse oximetry screening; arterial blood gas and lactate (metabolic acidosis); renal and liver function; glucose. ECG shows right ventricular dominance with reduced left-sided forces.
Imaging: Echocardiography is diagnostic: small or slit-like left ventricle, atretic or stenotic mitral and aortic valves, small ascending aorta with retrograde flow, size of the atrial communication and ductus. Chest X-ray: cardiomegaly and pulmonary venous congestion.

Differential diagnosis

Critical aortic stenosis or interrupted aortic arch
Severe coarctation of the aorta
Neonatal sepsis
Inborn errors of metabolism presenting with shock
Other cyanotic heart defects (transposition, TAPVR)

Goal of treatment

Keep the ductus open and balance pulmonary and systemic blood flow after birth, then convert to a single-ventricle (Fontan) circulation through staged surgery, or offer heart transplantation.

Treatment

Acute: Prostaglandin E1 infusion to keep the ductus arteriosus open; avoid excess supplemental oxygen and hyperventilation so that pulmonary flow does not steal from the systemic circulation; inotropes and ventilation as needed; urgent atrial septostomy if the septum is restrictive.
Surgical: Stage I (Norwood procedure, first week): the pulmonary trunk is used to build a new aorta, the atrial septum is opened and lung flow is supplied by a systemic-to-pulmonary shunt or a right ventricle-to-pulmonary artery conduit; a hybrid approach (ductal stent plus pulmonary artery bands) is an alternative.
Surgical: Stage II (bidirectional Glenn, around 3–6 months) connects the superior vena cava to the pulmonary arteries; stage III (Fontan, around 2–5 years) routes inferior vena cava blood to the lungs as well.
Surgical: Heart transplantation as an alternative, or when the staged circulation fails.
Follow-up: Nursing: apnoea and temperature monitoring on prostaglandin, oxygen saturation targets set by the team, feeding and weight gain; interstage home monitoring of saturation and weight with clear return criteria; lifelong congenital cardiology follow-up and neurodevelopmental assessment.

Complications

Death from shock if the ductus closes before treatment
Interstage sudden deterioration and death
Arrhythmias and failure of the single right ventricle; tricuspid regurgitation
Fontan complications: protein-losing enteropathy, plastic bronchitis, thrombosis, Fontan-associated liver disease
Neurodevelopmental delay

Prognosis

Without treatment it is fatal within the first weeks of life. With staged surgery most infants survive the first stage and many now reach adulthood, but the Fontan circulation is palliative and needs lifelong specialised follow-up; some patients eventually need transplantation.

Prevention

Prenatal ultrasound screening and fetal echocardiography to plan delivery at a cardiac surgical centre
Universal newborn pulse oximetry screening
Genetic counselling for families with previous left-sided heart defects

Test yourself

Think of the answer, then tap the question to see it.

On which structure does systemic blood flow depend in HLHS before surgery?

The ductus arteriosus.

Which drug is started immediately after diagnosis?

Prostaglandin E1, to keep the ductus open.

Why is high inspired oxygen avoided?

It lowers pulmonary resistance and diverts flow from the systemic circulation to the lungs.

What are the three stages of surgical palliation?

Norwood (stage I), bidirectional Glenn (stage II) and Fontan (stage III).

Which chromosomal syndrome in girls is associated with left-sided obstructive lesions including HLHS?

Turner syndrome (45,X).

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Educational information, not medical advice. For any symptom, see a health professional.

Sources: Hypoplastic left heart syndrome (MedlinePlus, US National Library of Medicine, 2026); Hypoplastic Left Heart Syndrome (HLHS) (Centers for Disease Control and Prevention (CDC), 2026).

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Representative model, for educational purposes only.

Left ventricle highlighted on the Durgical 3D model