Hypoplastic Left Heart Syndrome (HLHS)


What is hypoplastic left heart syndrome (HLHS)?

Hypoplastic left heart syndrome (HLHS) is a very complex heart condition seen in newborn babies. It is a single-ventricle heart defect, meaning one side of the heart is not developed correctly.

Babies born with HLHS have underdeveloped structures in the left side of the heart, including:

  • Left ventricle: The left ventricle or the lower left chamber of the heart is part of the heart that pumps out oxygen-rich blood to the aorta.
  • Aorta: The aorta is the largest blood vessel that carries blood from the heart to the rest of the body.
  • Mitral and aortic valves: Heart valves are flaps of tissue that open and close to control blood flow through the heart. The aortic valve allows blood to pass from the left ventricle to the aorta. The mitral valve controls blood flow from the top heart chamber (atrium) to the lower heart chamber (ventricle).

Anatomy of the heart | Cleveland Clinic

Normal anatomy in the left side of the heart.

How common is hypoplastic left heart syndrome?

Around one in 4,000 babies are born with hypoplastic left heart syndrome each year. It accounts for about 2% to 3% of all congenital heart diseases (CHD).

How does hypoplastic left heart syndrome affect a baby’s body?

In hypoplastic left heart syndrome, the heart’s left side is too small to pump enough blood to the rest of the body. The right ventricle or right lower chamber of the heart then takes over to pump blood to both lungs and whole body through a blood vessel called the ductus arteriosus. The ductus arteriosus is the vessel that all fetuses have and typically gets smaller until completely closing after babies are born. Without the ductus arteriosus, the condition is usually fatal if babies do not receive treatment.

Symptoms and Causes

What causes hypoplastic left heart syndrome (HLHS)?

Most of the time, there is no known cause for hypoplastic left heart syndrome. Sometimes, the cause of genetic. Babies with mutations (changes) in specific genes may have a higher risk of HLHS. These genes are known as GJA1 or NKX2-5.

What are the symptoms of hypoplastic left heart syndrome (HLHS)?

Newborns with HLHS don’t always show symptoms immediately. Instead, signs may develop within a few hours or days of birth.

Babies with hypoplastic left heart syndrome may experience:

  • Cyanosis, or a grayish (in dark-skinned people) or bluish (in light-skinned people) discoloration of skin, lips and nails.
  • Difficulty breathing.
  • Difficulty feeding.
  • Lack of energy (lethargy).
  • Rapid heartbeat.
  • Sweaty, clammy or cool skin.
  • Weak pulse.

Diagnosis and Tests

How is hypoplastic left heart syndrome diagnosed?

A healthcare provider may detect hypoplastic left heart syndrome during pregnancy or soon after the baby is born.

During pregnancy, healthcare providers use prenatal screening tools such as:

  • Ultrasound.
  • Fetal echocardiogram or ultrasound specifically perform to evaluate baby’s heart while in the uterus.

After the baby is born, healthcare providers diagnose the condition by observing symptoms and examining test results. Babies may have tests, including:

  • Chest X-ray: A chest X-ray shows the size and shape of the baby’s heart and lungs.
  • Echocardiogram: An ultrasound of the heart to evaluate internal heart structures.
  • Electrocardiogram (EKG): An electrocardiogram measures electrical changes during a heartbeat.
  • Pulse oximetry screening: Pulse oximetry measures how much oxygen is in the baby’s bloodstream.

Management and Treatment

How is hypoplastic left heart syndrome (HLHS) treated?

Initially, babies born with hypoplastic left heart syndrome will need a medication calls prostaglandin to keep the ductus arteriosus open and functioning. Patients will need a series of surgeries to direct appropriate blood flow to both lungs and body. Surgeons perform these operations in three stages:

Norwood procedure: Babies with HLHS need Norwood surgery within the first two weeks of life. During the procedure, surgeons:

  1. Build a new aorta by reconstructing the underdeveloped aorta to provide blood flow to the body.
  2. Place a shunt (tube) to reroute blood either from the right ventricle or the aorta to the blood vessel to the lungs (pulmonary arteries).
  3. Create a connection between the upper chambers of the heart to drain oxygen rich blood from the lungs to supply the body.

Bidirectional Glenn shunt operation: At four to six months of age, babies need a second operation. During the Glenn procedure, surgeons:

  1. Remove the old shunt.
  2. Place a new shunt to attach the superior vena cava to the pulmonary arteries. The superior vena cava (SVC) is a large vein that carries oxygen-poor blood from the upper body to the heart.
  3. Use this shunt to reduce the strain on the right ventricle by allowing blood to flow directly to the lungs.

Fontan procedure: Between 18 months and four years of age, babies need a final surgery. This final procedure allows all blood returning from the body to go straight to the lungs instead of mixing in the heart. During a Fontan procedure, surgeons will connect the inferior vena cava (IVC) to the pulmonary arteries. Similar to the SVC, the IVC is the large vein that carries oxygen-poor blood from the lower body to the heart.

Is a heart transplant a good treatment for hypoplastic left heart syndrome?

Sometimes, your baby’s surgeon may recommend a heart transplant instead of the three-part surgery series. Babies with heart transplants need lifelong medications. Discuss the pros and cons of heart transplants with your healthcare provider.

Can hypoplastic left heart syndrome (HLHS) be treated before birth?

Operating during pregnancy is not a treatment for hypoplastic left heart syndrome. A fetal surgeon may choose to operate only to correct some conditions that might be associated with poor HLHS outcomes or in patients who are developing HLHS.


Can I reduce the risk of hypoplastic left heart syndrome (HLHS)?

No obvious factors are known to cause HLHS. However, pregnant women are always encouraged to follow healthful habits during their pregnancy including:

Outlook / Prognosis

What is the outlook for babies with hypoplastic left heart syndrome?

The outlook for hypoplastic left heart syndrome depends on how complex the heart damage is. Ask your baby’s healthcare provider about the risks associated with each surgery.

Some children may have decreased physical endurance for the rest of their lives. Usually, healthcare providers recommend limiting physical activities such as competitive sports.

Are there long-term effects of hypoplastic left heart syndrome (HLHS)?

Children born with HLHS need lifelong follow-up with a cardiologist (heart doctor). These visits ensure that the heart, lungs and other organs continue to work properly. As they become adults, they will transition to care from a specialist in adult congenital heart disease.

Most children will need heart medications. They will also need to take antibiotics before any other surgeries, such as dental surgeries. These medications reduce the risk of endocarditis (a heart infection).

Living With

What else should I ask my healthcare provider?

If your baby has hypoplastic left heart syndrome, you may want to ask your healthcare provider:

  • What are the risks of surgery?
  • Are there potential surgery complications to watch for?
  • What medications does my child need?
  • Are there any medication side effects?
  • How will HLHS affect my child’s life?
  • What follow-up care does my child need after surgery?
  • If I have another baby, does that child have a higher risk of HLHS?

A note from Cleveland Clinic

Hypoplastic left heart syndrome is a condition that is present at birth. Babies born with HLHS need immediate treatment. Usually, treatment involves a series of three heart surgeries in a baby’s first few years of life. After these surgeries, most children need heart medication. Many children also need to limit intense physical activity. Children born with this condition can live a healthy life with long-term monitoring from a cardiologist.

Last reviewed by a Cleveland Clinic medical professional on 01/10/2021.


  • American Heart Association. Single Ventricle Defects. (https://www.heart.org/en/health-topics/congenital-heart-defects/about-congenital-heart-defects/single-ventricle-defects) Accessed 1/4/2020.
  • American Heart Association. Hypoplastic Left Heart Syndrome. (http://www.heart.org/idc/groups/heart-public/@wcm/@hcm/documents/downloadable/ucm_307664.pdf) Accessed 1/4/2020.
  • Centers for Disease Control and Prevention. Hypoplastic Left Heart Syndrome. (https://www.cdc.gov/ncbddd/heartdefects/hlhs.html) Accessed 1/4/2020.
  • National Center for Advancing Translational Sciences. Hypoplastic left heart syndrome. (https://rarediseases.info.nih.gov/diseases/6739/hypoplastic-left-heart-syndrome) Accessed 1/4/2020.
  • National Organization for Rare Disorders. Hypoplastic Left Heart Syndrome. (https://rarediseases.org/rare-diseases/hypoplastic-left-heart-syndrome/) Accessed 1/4/2020.

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