Hypoplastic Left Heart Syndrom (HLHS)

Hypoplastic left heart syndrome (HLHS) is a group of defects of the heart and large blood vessels. A child is born with this condition (congenital heart defect). It occurs when part of the heart doesn't develop as it should during the first 8 weeks of pregnancy.

In hypoplastic left heart syndrome, most of the left side of the heart is small and underdeveloped. These structures are usually affected:

  • Mitral valve. This is the valve that controls blood flow between the left atrium and left ventricle.
  • Left ventricle. This is the lower left chamber of the heart. It pumps blood to the body.
  • Aortic valve. The valve that controls blood flow from the left ventricle into the aorta, and then to the body.
  • Aorta. This is the large artery leading from the left ventricle to the body.

The left ventricle is normally very strong so it can pump blood to the body. When it is small and poorly developed, it can't pump enough blood out to the body. For this reason, an infant with hypoplastic left heart syndrome will not live long without surgery to fix the defect.