Hypoplastic Left Heart Syndrome

What is hypoplastic left heart syndrome?

Hypoplastic left heart syndrome is a medical condition that involves the under-development of the structures of the left side of the heart. The degree of under-development can vary from baby to baby but the structures involved usually include the following:

This illustration shows the normal heart structures.

What causes hypoplastic left heart syndrome?

Hypoplastic left heart syndrome occurs in four to 16 out of every 10,000 live births, and accounts for about 8 percent of congenital heart disease in babies. Under-development of the heart structures occurs during the first eight weeks of pregnancy. There is often no clear reason for the development of congenital heart defects. In some cases, there might be a genetic link or an environmental exposure that makes the defects occur more often in some families. In other cases, there is simply no known cause. Hypoplastic left heart syndrome occurs more often (55 percent to 70 percent) in males than females. Babies with this syndrome tend to also have other cardiovascular and neurologic organ defects.

This illustration shows some of the malformations seen in hypoplastic left heart syndrome, which includes a narrowing (in diameter) of the aorta; a pinching of the aorta; a narrowing or closure of the mitral and/or aortic valves; and underdevelopment of the left ventricle.

What are the symptoms of hypoplastic left heart syndrome?

Hypoplastic left heart syndrome can be detected while the baby is still in the uterus (see next question). However, once born, symptoms usually appear within a few days after birth. Symptoms, which might vary from baby to baby, include:

How is hypoplastic left heart syndrome diagnosed?

Diagnosis of this condition is made based on findings from a physical exam (listening to the heart and lungs), observation of symptoms (listed above), and the findings of other diagnostic tests listed below. Hypoplastic left heart syndrome can be diagnosed while the baby is still in the womb with the aid of an echocardiogram. This and other diagnostic tests are described below.

How is hypoplastic left heart syndrome treated?

Babies with this condition will die within days to weeks if not treated. Today, babies can be treated in a series of operations that re-route the function of the left side of the heart. Heart transplantation in another option though it is limited by the number of infant hearts available and the life-long need to take drugs to prevent organ rejection.

After birth

Once the baby is born, three surgical procedures timed to coincide with the development of the lungs, are performed and are described as follows:

The Norwood Procedure - This surgery, which re-routes the blood flow to avoid the left side heart problems, is performed shortly after birth. The surgery turns the right ventricle—the non-defective ventricle—into the main "workhorse" ventricle, able to pump blood to both the lungs and the body. The main pulmonary artery and the aorta are surgically connected with a shunt (tube), connecting a branch of the aorta to the pulmonary artery to supply blood to the lungs. Oxygenated blood is supplied to the body through other branches of the aorta.

Bi-directional Glenn Operation - This operation usually is performed about three to eight months after the Norwood procedure, when the lungs are more mature and don't require ventricular force to send blood to the lungs. During this operation, the shunt to the pulmonary arteries is disconnected and a new shunt connects the superior vena cava to the pulmonary artery. This new shunt diverts half of the de-oxygenated blood directly to the lungs without the need to go through the ventricle.

Fontan Operation - This operation usually is performed about 18 to 36 months after the Glenn operation, a time when the lungs have further matured and the vessels of the lungs can accommodate all the de-oxygenated blood from the lower part of the body. This operation connects the inferior vena cava—the major blood vessel that carries de-oxygenated blood from the lower part of the body back to the heart—with the pulmonary artery. This is done by creating a channel through or just outside the heart to direct blood to the pulmonary artery. After this operation, blood flows passively through the lungs, and the single ventricle pumps exclusively oxygenated blood to the body.

The decision regarding which surgical approach to take will depend on the baby's overall health, extent of disease, surgeon's expertise, expectations about how the baby's disease might progress, and parental opinion. Because these surgeries are complex and need to be individualized for each baby, your heart doctor will help you decide which medical and surgical approach will be best for your baby.

Prior to birth

Treatment of hypoplastic left heart syndrome in utero (in the developing fetus) is a new approach being explored. Following are two emerging treatment strategies. In a small subset of fetuses in which the hole between the atria is closed, a new procedure that opens the hole before the baby is born has been developed. This new procedure is known as fetal balloon atrial septostomy.

There is another subset of children who develop a problem with the aortic valve that then leads to enlargement of the left ventricle. The left ventricle then shrinks causing hypoplastic left heart syndrome. One proposed surgical strategy is to open the aortic valve before the left ventricle shrinks.

How successful are the various treatment options? Can my child expect to have a full normal length of life?

Ask your heart doctor about the specific outlook to expect for your baby. The outlook varies from baby to baby depending on the issues mentioned above. In addition, each stage of the different surgical repair procedures carries different risks and complications. Also, the outcomes at each medical facility itself are different based on the number of cases performed and the surgeon's experience. Be sure to ask your heart doctor about these concerns.

Children with hypoplastic left heart syndrome require check-up appointments throughout their lives to evaluate how well their hearts are working. Nearly all children will require heart medicines as well as antibiotics prior to dental work or other surgeries to reduce the risk of infection to the heart valves (a condition called endocarditis).


This information is provided by the Cleveland Clinic and is not intended to replace the medical advice of your doctor or health care provider. Please consult your health care provider for advice about a specific medical condition. For additional health information, please contact the Center for Consumer Health Information at the Cleveland Clinic (216) 444-3771 or toll-free (800) 223-2273 extension 43771. If you prefer, you may visit www.clevelandclinic.org/health/ or www.clevelandclinicflorida.org. This document was last reviewed on: 2/14/2017