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What is hypoplastic left heart syndrome? (HLHS)

Hypoplastic left heart syndrome (HLHS) is a severe congenital heart defect in which the left side of the heart is underdeveloped.


In a normal heart , the heart's left side has the job of pumping oxygenated blood into the aorta, the large artery that carries blood to the body. In a child with HLHS:


  • The mitral valve, which separates the two left chambers of the heart, is too small or completely closed (atretic).

  • The left ventricle (the lower, pumping chamber) is very small.

  • The aortic valve, which separates the left ventricle and the aorta, is too small or completely closed (atretic).

Care Required
Between the Norwood and Glenn operations

Though early outcomes for patients with single ventricle heart defects after staged reconstruction have improved dramatically, the period between the Norwood procedure and the Glenn operation remains a very vulnerable time for infants. The Children's Hospital of Philadelphia created the Infant Single Ventricle Monitoring Program to focus on the care and monitoring of infants with single ventricle heart defects, such as HLHS, between the first and second reconstructive surgeries.

Through age 18

Frequent appointments with your child’s cardiologist in infancy and early childhood are important to minimize risk factors associated with single ventricle heart defects. Your child will need a customized series of diagnostic tests between the planned stages of surgery.


Once the surgeries are complete, your child will have appointments with a pediatric cardiologist once a year or more frequently. It is also possible that your child will require additional surgical or catheter therapies, or in rare cases heart transplantation. 


Most children will not be required to take medication regularly, though some patients may need to take aspirin every day to “thin” the blood. 


When it comes to physical activities, in most cases, parents are told to allow the child to do as much as he or she is able to do. Most children will self-limit (stop activity if it begins to stress the body). There are also certain sports and activities to avoid. Your team will discuss these with you based on your child’s unique situation.

Signs and Symptoms

The following symptoms of hypoplastic left heart syndrome may be present at birth or several days later:


  • Blue or purple tint to lips, skin and nails (cyanosis)

  • Difficulty breathing

  • Difficulty feeding

  • Lethargy (Sleepy or unresponsive)


Hypoplastic left heart syndrome is most often fatal without early intervention. Compared to 25 years ago, there are now many different options for treatment of this complex heart condition; an individualized approach is taken for each and every child.


Typically, the child will require open heart surgery to re-direct the oxygen-rich ("red") blood and oxygen-poor ("blue") blood. After these operations:

  • The right side of the heart will do what is usually the job of the left side — pumping oxygenated blood to the body.

  • The deoxygenated blood will flow from the veins to the lungs without passing through the heart.


The series of three reconstructive operations to repair HLHS — the Norwood, Glenn and Fontan procedures — is known as " Staged Reconstruction ."


Frequent surveillance in infancy and early childhood is important to minimize risk factors for the eventual Fontan operation. The child will also need a customized series of diagnostic tests between the planned stages of surgery, and throughout childhood. Additional surgical or catheter therapies, or in rare cases heart transplantation, may also be recommended.

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