Hypoplastic left heart syndrome (HLHS)

Hypoplastic left heart syndrome (HLHS)


Hypoplastic left heart syndrome (HLHS) is a rare, complex, serious form of congenital heart disease composed of multiple findings resulting in small left-sided heart structures. It is called a “single-ventricle heart defect,” because the left ventricle, which needs to be strong enough to support an infant's circulation, is underdeveloped and cannot function effectively, leaving just one pumping chamber. The right chamber then overworks and eventually the heart will fail.
Other left-sided structures — including the mitral valve, aortic valve and ascending aorta — can be underdeveloped to varying degrees.


As is often the case with congenital heart defects, there is no known cause. However, 10 percent of infants with HLHS also have other birth defects.



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

  • 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

Risk factors

HLHS is found more often in male infants than in females.


A regular prenatal ultrasound may indicate a problem that requires further testing with a fetal echocardiogram using a specialized ultrasound to create pictures of the developing heart. Other tests that may be prescribed are:

  • Electrocardiogram
  • Chest X-rays
  • Cardiac catheterization
  • Pulse oximetry, which measures the level of oxygen in the bloodstream


If the infant is cyanotic (has skin or membranes that appear blue or purple), it requires intensive support prior to surgical intervention. A staged surgical approach requiring multiple operations 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 are:

  • Stage 1: Norwood procedure
  • Stage 2: Bi-directional cavopulmonary anastomosis
  • Stage 3: Fontan (operation)

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