Hypoplastic left heart syndrome (HLHS)

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Learn about hypoplastic left heart syndrome (HLHS). This condition involves the left side of the heart being underdeveloped, and is extremely serious.

Key points

  • Hypoplastic left heart syndrome (HLHS) is the most common severe congenital heart defect.
  • Symptoms of HLHS usually appear soon after birth.
  • HLHS cannot be corrected, but reconstructive heart surgery can usually help the baby live and grow.
  • HLHS can be fatal if untreated, but survival improves after each surgery for the condition.

With hypoplastic left heart syndrome (HLHS), the left side of the heart is underdeveloped. Blood coming back to the heart from the lungs has to go through an atrial septal defect, and blood reaches the aorta through a patent ductus arteriosus.

The two images below compare a normal heart to a heart with HLHS.

Normal heartNormal heart showing placement of the atria, ventricles, aorta, superior vena cava, inferior vena cava, pulmonary artery and pulmonary veins
The heart has two upper (receiving) and two lower (pumping) chambers. Blood flows into the upper chambers (the right atrium and the left atrium). The lower chambers (the right and left ventricles) pump blood out of the heart. The heart valves open and close to keep blood flowing in the correct direction.
Hypoplastic left heart syndromeHeart showing small aorta, right atrium, atrial septal defect, right ventricle, small left ventricle, aortic valve, mitral valve, and patent ductus arteriosus.
Hypoplastic left heart syndrome happens when the aortic and/or mitral valves fail to develop, resulting in a left ventricle and aorta that are too small to effectively pump blood to the body. The right ventricle becomes the only pumping chamber of the heart (single ventricle circulation). The right ventricle has to pump blood to the pulmonary artery and the aorta through the PDA.

HLHS is the most common of the severe congenital heart defects. It accounts for 7% to 9% of all heart defects diagnosed within the first year of life.

What are the symptoms of hypoplastic left heart syndrome?

Symptoms usually become noticeable soon after birth when the ductus ateriosus closes. They include cyanosis, poor colour, rapid difficult breathing, and trouble eating. The condition can be fatal if left untreated. An electrocardiogram and an echocardiogram are done to make a diagnosis.

How is hypoplastic left heart syndrome treated?

At first, a drug like prostaglandin will be given to keep the ductus arteriosus open to improve blood flow. HLHS cannot be corrected, but reconstructive heart surgery can usually help the baby live and grow. Three operations are done in stages, to help the body and lungs adjust to the altered blood flow. They include:

  • the Norwood procedure
  • the bidirectional cavopulmonary shunt (BCPS)
  • the Fontan operation

The goal is to help the right ventricle pump only oxygenated blood to the body and prevent it from mixing with de-oxygenated blood.

Heart transplantation may also be considered as an alternative surgical option.

What is the long-term outlook for children with hypoplastic left heart syndrome?

It is estimated that 75% of children with HLHS survive after the first stage of the reconstruction. Survival improves with each subsequent surgical procedure.

Last updated: December 4th 2009