Hypoplastic left heart syndrome !

Malformation

The left side of the heart is too small to pump to the body; the baby depends on the ductus arteriosus to survive.

Updated 2026-11-01

See it in 3D: Left ventricle · Mitral anterior leaflet · Mitral posterior leaflet · Ascending aorta · Aortic arch · Interatrial septum · Ligamentum arteriosum

What it is

In hypoplastic left heart syndrome the left ventricle, mitral valve, aortic valve and ascending aorta are underdeveloped. The right ventricle pumps both to the lungs and, through the ductus arteriosus, to the body, while left atrial blood returns across the foramen ovale. When the ductus closes shock follows, so it is a critical duct-dependent defect.

Embryological cause

Heart chambers grow with the blood that flows through them in fetal life.
Early obstruction of the mitral or aortic valve, or a restrictive foramen ovale, cuts flow to the left ventricle.
With little flow, the left ventricle and ascending aorta fail to grow and the wall may turn fibrotic.
The genetic cause is heterogeneous; it also appears in syndromes such as Turner.

Markers

Fetal blood flow
Turner syndrome (association)

How it presents

A newborn who looks well and within hours or days develops fast breathing, gray pallor and weak pulses.
Cardiogenic shock and metabolic acidosis as the ductus closes.
Mild cyanosis from atrial mixing.

Diagnosis

Prenatal ultrasound: the four-chamber view shows a tiny left ventricle.
Fetal echocardiography to confirm and plan delivery at a center with heart surgery.
Newborn pulse oximetry.

Test yourself

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

Which structures are underdeveloped in hypoplastic left heart syndrome?

The left ventricle, mitral valve, aortic valve and ascending aorta.

Why does a newborn with hypoplastic left heart go into shock after a few days?

Because flow to the body depended on the ductus arteriosus, and it closes.

Which mechanism explains the poor growth of the left ventricle?

Low blood flow through the left side in fetal life, from valve obstruction or a restrictive foramen ovale.

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See it in 3D

The structures of Durgical's 3D anatomy where it is found.

← All of embryology

Educational content on embryonic development; not a guide to prenatal diagnosis or to medicines in pregnancy and no substitute for a health professional's advice. No doses are given.

Sources: Langman's Medical Embryology, 13th ed., ch. 13: Cardiovascular System (Wolters Kluwer, 2015); Hypoplastic Left Heart Syndrome (HLHS) | Congenital Heart Defects (CHDs) | CDC (Centers for Disease Control and Prevention, 2024).

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Representative model, for educational purposes only.