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Hypoplastic left heart syndrome (HLHS) is a rare, complex, serious form of congenital heart disease in which the left ventricle (or chamber) of the heart is underdeveloped. As a result, HLHS is called a “single-ventricle heart defect.” Without treatment, the right chamber becomes overworked, which eventually leads to heart failure.

Some infants with HLHS may also have other birth defects. For example, other left-sided structures — including the mitral valve, aortic valve and ascending aorta — can be compromised. HLHS is found more often in male infants than in females.


As is often the case with congenital heart defects, there is no known cause of hypoplastic left heart syndrome. 


Symptoms manifest within a few days of birth if left untreated. They include:

  • Pale skin color
  • Cyanosis — blue-tinged skin, lips, and nailbeds, caused by lack of oxygen in the bloodstream
  • Difficult or fast breathing
  • Difficulty in feeding
  • Rapid heartbeat
  • Skin that is cool, clammy, or sweaty to the touch
  • Cold limbs
  • Fatigue, lethargy
  • Weak pulse

Diagnosis & testing

A standard prenatal ultrasound may indicate a problem that requires further testing with a fetal echocardiogram. A fetal echocardiogram is a specialized ultrasound to create pictures of the developing heart.

Treatment options

If the infant is cyanotic (has skin or membranes that appear blue or purple), it requires intensive support prior to surgical intervention. A surgical approach requiring multiple operations – known as staged reconstruction- is necessary to redirect blood flow through the heart. Often, cardiac catheterization is performed prior to each operation to assess the child's circulation. The three stages of staged reconstruction are:

  • Stage 1: Norwood procedure. Performed in the first week of life, this procedure reconfigures the ventricles so that the right chamber can act as the main “pump” both into and out of the heart.
  • Stage 2: Bidirectional cavopulmonary anastomosis. Sometimes known as the bidirectional Glenn procedure or the hemi-Fontan procedure, this procedure is performed at around 4 to 6 months of age. It reroutes the patient’s circulation so that deoxygenated blood from the brain can drain into the lungs and deliver oxygenated blood to the organs.
  • Stage 3: Fontan procedure. Usually performed between the ages of 18 months and 3 years, the Fontan procedure reroutes blood flow from the lower body to the lungs by creating a channel outside of the heart. This channel is joined with the connection made in the Glenn procedure. 
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