Hypoplastic Left Heart Syndrome

Hypoplastic left heart syndrome (HLHS) is a complex and rare heart condition that’s present at birth (congenital). It’s a single-ventricle heart defect. This means one side of your baby’s heart didn’t develop correctly.

In babies born with hypoplastic left heart syndrome, some structures in the left side of their heart didn’t develop completely, including:

• Left ventricle: This is your heart’s lower left chamber, which pumps oxygen-rich blood to your aorta.
• Aorta: This is your largest blood vessel. It takes blood from your heart to the rest of your body.
• Mitral and aortic valves: These flaps of tissue open and close to control how your blood moves through your heart. Your aortic valve allows blood to pass from your left ventricle to your aorta. Your mitral valve controls blood flow from your top heart chamber (atrium) to your lower heart chamber (ventricle).

Also, a baby with hypoplastic left heart syndrome may have an opening (atrial septal defect) between the two upper heart chambers. Normally, this would be a solid wall of tissue.

Hypoplastic left heart syndrome vs. normal heart

Each side of a normal heart has a job. The right side moves oxygen-poor blood to your lungs to get oxygen. The left side sends oxygen-rich blood to your body.

In a baby with hypoplastic left heart syndrome, the heart’s left side is too small to pump enough blood to the rest of the body. Their right ventricle or right lower chamber of their heart then takes over to pump blood to both their lungs and whole body. It does this through a blood vessel called the ductus arteriosus.

The ductus arteriosus is a vessel that all fetuses have. It typically gets smaller until it closes soon after birth. With a closed ductus arteriosus, hypoplastic left heart syndrome is usually fatal if babies don’t receive treatment.

How common is hypoplastic left heart syndrome?

About 1 in 3,800 babies are born with hypoplastic left heart syndrome each year in the U.S. This condition accounts for about 2% to 3% of all congenital heart diseases (CHD). Hypoplastic left heart syndrome affects more men and people assigned male at birth (67%) than women and people assigned female at birth.