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Hypoplastic Left Heart Syndrome



Hypoplastic left heart syndrome (HLHS) is a rare heart defect. Structures on the left side of the heart, such as the aorta, aortic valve, left ventricle, and mitral valve, may be too small, missing, or poorly formed. This lowers oxygen-rich blood flow to the body.

Heart Chambers and Valves
heart anatomy

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Blood Flow Through the Heart

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HLHS is present at birth. It is caused by a genetic defect. It is not known why the heart does not develop the right way.

Risk Factors

Things that may raise the risk of having a child with HLHS are:

  • People in your family who have congenital heart defects
  • Prior pregnancy with fetal heart problems or miscarriage


These problems often appear within days after birth:

  • Blue/gray skin color
  • Cool skin
  • Problems breathing
  • Sweaty, clammy skin
  • Poor feeding


The diagnosis may be suspected during a prenatal ultrasound.

If the diagnosis was not made before birth, the doctor will ask about your child's symptoms and health history. A physical exam will be done.

Pictures may be taken of your child's chest. This can be done with an echocardiogram. This can confirm the diagnosis.


Some defects are hard to treat. Some options are:

  • Temporary medicines to help with blood flow
  • Supportive care, such as IV fluids, a feeding tube, or help with breathing
  • A series of surgeries that allow the right ventricle do the work of two ventricles

Children with this heart problem will need lifelong monitoring by a doctor who treats heart problems.


There are no known guidelines to prevent this health problem.


American Heart Association

Family Doctor—American Academy of Family Physicians


Canadian Cardiovascular Society

Heart and Stroke Foundation of Canada


Feinstein JA, Benson DW, et al. Hypoplastic left heart syndrome: current considerations and expectations. J Am Coll Cardiol. 2012 Jan 3;59(1 Suppl):S1-S42, correction can be found in J Am Coll Cardiol 2012 Jan 21;59(5):544.

Hypoplastic left heart syndrome. EBSCO DynaMed website. Available at: Updated September 11, 2017. Accessed December 18, 2020.

Single ventricle defects. American Heart Association website. Available at: Accessed December 18, 2020.

Last reviewed September 2020 by EBSCO Medical Review Board Chelsea Skucek, MSN, BS, RNC-NIC