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What is hypoplastic left heart syndrome (HLHS)?

Hypoplastic left heart syndrome (HLHS) is a serious heart problem present at birth. In HLHS, the left side of the heart — including the aorta, aortic valve, left ventricle and mitral valve — does not fully develop. Because of this, the heart cannot pump enough oxygen-rich blood to the body.

What causes HLHS?

The exact cause of HLHS is usually unknown. Some children with HLHS can have other congenital heart defects.

How does HLHS affect the heart?

Before birth, normal openings in the heart and the ductus arteriosus allow blood to bypass the lungs. In babies with HLHS, these normal fetal connections allow blood to reach the body because the left side of the heart cannot pump blood effectively. After birth, as these openings begin to close, blood flow to the body becomes severely limited.

Babies with HLHS often seem healthy at birth. Within days, they may develop:

• Trouble breathing
• Fast breathing
• Difficulty feeding
• Pale, gray or bluish skin color
• Weak pulse

Without treatment, HLHS is life-threatening. 

How is HLHS treated?

HLHS cannot be fully corrected, but treatment can help the heart work more effectively. Most babies need a series of surgeries shortly after birth. Some children may be candidates for a heart transplant. Your child’s cardiology team will discuss treatment options that are best for your child.

Treatment often includes three surgeries:

1. The Norwood procedure, performed soon after birth: This surgery reconstructs the aorta so the right ventricle can pump blood to the body. Blood flow to the lungs is provided through either a Blalock-Taussig shunt or a Sano shunt.
2. The Glenn (or hemi-Fontan) procedure, usually performed between 4 and 8 months
3. The lateral tunnel Fontan or extracardiac Fontan procedure, usually performed between 18 months and 3 years

Together, these surgeries gradually redirect low-oxygen blood returning from the body directly to the pulmonary arteries, reducing the workload of the single ventricle. The goal is to improve blood flow to the lungs and body, reduce cyanosis (low blood oxygen levels), and allow the right ventricle to pump oxygen-rich blood to the body. Some infants need additional procedures between these surgeries.

Some doctors recommend a heart transplant for children with HLHS. A transplant can provide a heart with a normal structure, but it requires lifelong medications to prevent rejection.

Other transplant-related complications can occur, so it is important to discuss the benefits and risks with your child’s doctor.

Hypoplastic left heart syndrome in children: What families need to know

What activities can my child do?

Children with HLHS may need to limit physical activity based on their endurance and overall heart function. Some competitive sports may pose increased risks. Your child’s pediatric cardiologist can help determine which activities are safe and appropriate for them.

What will my child need in the future?

Children with HLHS need lifelong care from a cardiologist to monitor how their heart is working over time. Regular follow-up visits help identify changes in heart function and guide treatment decisions.

Many children with HLHS will need ongoing treatment as they grow. These may include:

• Heart medications
• Heart catheterization procedures
• Additional surgeries or interventions as they grow

What about preventing endocarditis?

Some children with HLHS have a higher risk of developing endocarditis, an infection of the heart. Ask your child’s pediatric cardiologist about whether they need antibiotics before certain dental procedures to help prevent endocarditis. Learn more in the Endocarditis section.

Hypoplastic left heart syndrome in adults: What to expect

Almost all adults with HLHS have had one or more surgeries during childhood. Many have had a series of procedures to improve blood flow through the heart and lungs.

The surgeries help redirect oxygen-poor blood flow to the lungs while allowing the heart’s single working ventricle to pump blood to the body. While these procedures improve circulation, the heart does not function the same way as a typical two-ventricle heart. As a result, some people may develop health problems over time related to blood flow through the heart and lungs. Lifelong follow-up care is important.

Problems You May Have

Many adults with HLHS live active and productive lives. However, because the heart functions differently than a two-ventricle heart, some people develop health problems over time.

Possible complications include:

• Abnormal heart rhythms (arrhythmias), including heartbeats that are too fast, too slow or irregular
• Fluid buildup, especially in the abdomen, legs or feet. Some people may also develop varicose veins
• Changes in heart function, including weakening of the heart muscle
• Blood clots that may require treatment with anticoagulation medication

Ongoing Care

What will I need in the future?

Because HLHS is a complex congenital heart defect, you should receive lifelong care from a cardiologist who specializes in adult congenital heart disease. You should also talk with your cardiologist before any non-heart surgery or invasive procedure.

Medical follow-up

Regular follow-up visits help monitor your heart health and identify problems early. Many people with HLHS take one or more medications as part of their ongoing care.

You will need regular follow up visits, often at least once a year, although some people need more frequent care. Your cardiologist may recommend tests such as:

• Electrocardiogram (EKG)
• Echocardiogram
• Cardiac MRI
• Holter or other heart rhythm monitoring
• Exercise stress testing
• Cardiac catheterization

These tests help your care team monitor heart function and guide treatment decisions.

Activity Restrictions

You may need to limit some activities, particularly competitive sports. If you have decreased heart function or heart rhythm problems, you may need more activity restrictions. Your cardiologist can help you determine which activities are safe for you.

Learn more in the Physical Activity section.

Endocarditis Prevention

You may need antibiotics before certain dental procedures to help prevent endocarditis, an infection of the heart. Talk with your cardiologist about your risk and whether preventive antibiotics are recommended.

Learn more in the Endocarditis section.

Pregnancy

Some women who have had a Fontan procedure can become pregnant and safely carry a pregnancy to term. However, pregnancy may carry higher risks if you have a weakened heart muscle, a blockage or blood clot in the Fontan connection or heart rhythm problems.

If you are considering pregnancy, talk with your cardiologist before conception to understand your risks and plan your care. You should also receive care from a high-risk obstetrician who has experience caring for people with congenital heart disease during pregnancy and delivery.

Learn more in the Pregnancy section.

Will I need additional procedures or surgery?

Most people with HLHS have their major surgeries during early childhood, although some will need additional surgeries later in life to treat complications.

Additional treatment may include:

• Closing openings in the heart
• Implanting a pacemaker
• Repairing or replacing a heart valve that is not working properly

In rare cases, a heart transplant may be considered. Your cardiologist can explain which treatments may be appropriate for your condition.