What Is Hypoplastic Left Heart Syndrome?

Hypoplastic left heart syndrome (HLHS) is a rare, complex form of congenital heart disease that affects more than 2,000 newborns every year in the United States. In HLHS, the left side of a child's heart — the left ventricle, ascending aorta and left heart valves — is severely underdeveloped. The result is a heart with only a single functional ventricular chamber — the right ventricle — and a small ascending aorta.

In a properly developed heart, the right side pumps blood to the lungs, while the left side pumps blood to the rest of the body. In newborns with HLHS, the right side of the heart is forced to do double duty and pump blood to both the lungs and the rest of the body.

HLHS occurs during fetal growth when the baby's heart is developing; its cause is unknown, and it cannot be prevented. Once an initial diagnosis of HLHS is made, available therapeutic options remain palliative — there is no cure.

Without treatment — generally a three-stage surgery, with the first one done within a week of the baby being born — the disease is fatal soon after birth.

Read more about HLHS in the program brochure (PDF).