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Hypoplastic left heart syndrome (HLHS) is a birth defect that affects normal blood flow through the heart. As the baby develops during pregnancy, the left side of the heart does not form correctly. Hypoplastic left heart syndrome is one type of congenital heart defect. Congenital means present at birth.
Hypoplastic left heart syndrome affects a number of structures on the left side of the heart that do not fully develop, for example:

• The left ventricle is underdeveloped and too small.
• The mitral valve is not formed or is very small.
• The aortic valve is not formed or is very small.
• The ascending portion of the aorta is underdeveloped or is too small.
• Often, babies with hypoplastic left heart syndrome also have an atrial septal defect, which is a hole between the left and right upper chambers (atria) of the heart.

The Centers for Disease Control and Prevention (CDC) estimates that each year about 960 babies in the United States are born with hypoplastic left heart syndrome.¹ In other words, about 1 out of every 4,344 babies born in the United States each year is born with hypoplastic left heart syndrome




Surgery
Soon after a baby with hypoplastic left heart syndrome is born, multiple surgeries done in a particular order are needed to increase blood flow to the body and bypass the poorly functioning left side of the heart. The right ventricle becomes the main pumping chamber to the body. These surgeries do not cure hypoplastic left heart syndrome, but help restore heart function. Sometimes medicines are given to help treat symptoms of the defect before or after surgery. Surgery for hypoplastic left heart syndrome usually is done in three separate stages:

1. Norwood Procedure
   This surgery usually is done within the first 2 weeks of a baby’s life. Surgeons create a “new” aorta and connect it to the right ventricle. They also place a tube from either the aorta or the right ventricle to the vessels supplying the lungs (pulmonary arteries). Thus, the right ventricle can pump blood to both the lungs and the rest of the body. This can be a very challenging surgery. After this procedure, an infant’s skin still might look bluish because oxygen-rich and oxygen-poor blood still mix in the heart.
   
2. Bi-directional Glenn Shunt Procedure
   This usually is performed when an infant is 4 to 6 months of age. This procedure creates a direct connection between the pulmonary artery and the vessel (the superior vena cava) returning oxygen-poor blood from the upper part of the body to the heart. This reduces the work the right ventricle has to do by allowing blood returning from the body to flow directly to the lungs.
   
3. Fontan Procedure
   This procedure usually is done sometime during the period when an infant is 18 months to 3 years of age. Doctors connect the pulmonary artery and the vessel (the inferior vena cava) returning oxygen-poor blood from the lower part of the body to the heart, allowing the rest of the blood coming back from the body to go to the lungs. Once this procedure is complete, oxygen-rich and oxygen-poor blood no longer mix in the heart and an infant’s skin will no longer look bluish.

Infants who have these surgeries are not cured; they may have lifelong complications.
Infants with hypoplastic left heart syndrome will need regular follow-up visits with a cardiologist (a heart doctor) to monitor their progress. If the hypoplastic left heart syndrome defect is very complex, or the heart becomes weak after the surgeries, a heart transplant may be needed. Infants who receive a heart transplant will need to take medicines for the rest of their lives to prevent their body from rejecting the new heart.