Hypoplastic Left Heart Syndrome (HLHS)

This congenital heart condition occurs when the left side of the heart does not develop normally. It is a rare and complex condition that results in an inadequate supply of oxygenated blood to the body. The condition may be diagnosed during pregnancy with ultrasound, or after birth with an echocardiogram.

Normal Heart

In a normal heart, oxygen-depleted blood returns from the body to the right atrium. It empties into the right ventricle, which then pumps the blood to the lungs where it will be oxygenated. This oxygenated blood from the lungs returns to the heart’s left atrium and is pumped out to the body through the left ventricle.

Heart with HLHS

In a heart with HLHS, the left ventricle is underdeveloped and cannot function normally. Other structures in the heart may also be affected. The mitral valve and the aortic valve may be abnormally small or may not open at all, the aorta may be reduced in size, and there is usually a hole in the wall between the left and right atria.


Symptoms of HLHS may be present shortly after birth. Newborns with HLHS may have a heart murmur, gray-blue skin, and low blood pressure. Without treatment, HLHS is fatal within the first days or weeks of life.


HLHS is initially treated with a medication that affects the ductus arteriosus – a blood vessel between the aorta and pulmonary artery. This vessel normally closes soon after birth, but the medication keeps it open to help oxygenated blood travel out to the body. After the newborn is stabilized, a series of surgeries or a heart transplant will be needed.