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Hypoplastic Left Heart Syndrome (HLHS)

Hypoplastic left heart syndrome is a complex and rare heart defect present at birth (congenital). In this condition, the left side of the heart is critically underdeveloped.

If your baby is born with hypoplastic left heart syndrome, the left side of the heart can't effectively pump blood to the body. Instead, the right side of the heart must pump blood to the lungs and to the rest of the body.

Medication to prevent closure of the connection (ductus arteriosus) between the right and left sides, followed by either surgery or a heart transplant, is necessary to treat hypoplastic left heart syndrome. Advances in care have improved the outlook for babies born with this condition.


Babies born with hypoplastic left heart syndrome usually are seriously ill soon after birth. Signs and symptoms include:

  • Greyish-blue skin colour (cyanosis)
  • Rapid, difficult breathing
  • Poor feeding
  • Cold hands and feet
  • Weak pulse
  • Being unusually drowsy or inactive

If the natural connections between the heart's left and right sides (foramen ovale and ductus arteriosus) are allowed to close in the first few days of life in babies with hypoplastic left heart syndrome, they can go into shock and possibly die.

Signs of shock include:

  • Cool, clammy skin that can be pale or grey
  • A weak and rapid pulse
  • Abnormal breathing that may be either slow and shallow or very rapid
  • Lacklustre eyes that seem to stare

A baby in shock might be conscious or unconscious. If you suspect your baby is in shock, immediately call 911 or your local emergency number.

When to see a doctor

It's likely that your baby would be diagnosed with hypoplastic left heart syndrome either before birth or soon after. However, you should seek medical help if you notice that your baby has any of the signs or symptoms of the condition.



Before birth

It's possible for a baby to be diagnosed with hypoplastic left heart syndrome while still in the womb. Your doctor might be able to identify the condition on a routine ultrasound exam during the second trimester of pregnancy.

After birth

After your baby is born, a doctor might suspect a heart defect, such as hypoplastic left heart syndrome, if your baby has grayish-blue skin color or has trouble breathing. Your baby's doctor might also suspect a heart defect if he or she hears a heart murmur — an abnormal sound caused by turbulent blood flow — when listening to the heart with a stethoscope.

Doctors usually use an echocardiogram to diagnose hypoplastic left heart syndrome. This test uses sound waves that bounce off your baby's heart to produce moving images that can be viewed on a video screen.

If your baby has hypoplastic left heart syndrome, the echocardiogram will show a smaller than normal left ventricle and aorta. The echocardiogram might also show abnormal heart valves.

Because this test can track blood flow, it also shows blood moving from the right ventricle into the aorta. In addition, an echocardiogram can identify associated heart defects, such as an atrial septal defect.



Hypoplastic left heart syndrome occurs when the baby's heart is developing in the womb. The cause is unknown. However, if your family has one child with hypoplastic left heart syndrome, the risk of having another with a similar condition is increased.

A normal heart has four chambers, two on the right and two on the left. In performing its basic job — pumping blood throughout the body — the heart uses its left and right sides for different tasks.

The right side moves blood to the lungs. In the lungs, oxygen enriches the blood, which then circulates to the heart's left side. The left side of the heart pumps blood into a large vessel called the aorta, which circulates the oxygen-rich blood to the rest of the body.

What happens in hypoplastic left heart syndrome

In hypoplastic left heart syndrome, the left side of the heart can't properly supply blood to the body because the lower left chamber (left ventricle) is too small or in some cases doesn't exist. In addition, the valves on the left side of the heart (aortic valve and mitral valve) don't work properly, and the main artery leaving the heart (aorta) is smaller than normal.

For the first days of life, the right side of the heart can pump blood both to the lungs and to the rest of the body through a blood vessel that connects the pulmonary artery directly to the aorta (ductus arteriosus). The oxygen-rich blood returns to the right side of the heart through a natural opening (foramen ovale) between the right chambers of the heart (atria). When the foramen ovale and the ductus arteriosus are open, they are referred to as being "patent."

If the ductus arteriosus and the foramen ovale close — which they normally do after the first day or two of life — the right side of the heart has no way to pump blood out to the body. In babies with hypoplastic left heart syndrome, medication is necessary to keep these connections open and keep blood flowing to the body until heart surgery is performed.


Risk factors

If you already have a child with hypoplastic left heart syndrome, you have a higher risk of having another baby with this or a similar condition.

Beyond family history, there are no clear risk factors for hypoplastic left heart syndrome.



Without surgery, hypoplastic left heart syndrome is deadly, usually within the first few days or weeks of life.

With treatment, many babies survive, although most will have complications later in life. Some of the complications might include:

  • Tiring easily when participating in sports or other exercise
  • Heart rhythm problems (arrhythmias)
  • Fluid build-up in the lungs, abdomen, legs and feet (oedema)
  • Growth restriction
  • Formation of blood clots that may lead to a pulmonary embolism or stroke
  • Developmental problems related to the brain and nervous system
  • Need for additional heart surgery or transplantation


There's no way to prevent hypoplastic left heart syndrome. If you have a family history of heart defects, or if you already have a child with a congenital heart defect, consider talking with a genetic counsellor and a cardiologist experienced in congenital heart defects before getting pregnant.



Hypoplastic left heart syndrome is treated through several surgical procedures or a heart transplant. Your child's doctor will discuss treatment options with you.

If the diagnosis has been made before the baby is born, doctors usually recommend delivery at a hospital with a cardiac surgery centre.

Your baby's doctor might recommend several options to help manage your baby's condition before surgery or transplant, including:

  • Medication. The medication alprostadil (Prostin VR Paediatric) helps widen the blood vessels and keeps the ductus arteriosus open.
  • Breathing assistance. If your baby has trouble breathing, he or she may need help from a breathing machine (ventilator) to get enough oxygen.
  • Intravenous fluids. Your baby will receive fluids through a tube inserted into a vein.
  • Feeding tube. If your baby has trouble feeding or tires while feeding, he or she can be fed through a feeding tube.
  • Atrial septostomy. This procedure creates or enlarges the opening between the heart's upper chambers (atria) to allow more blood flow from the right atrium to the left atrium if the foramen ovale closes or is too small. If your baby already has an atrial septal defect, an atrial septostomy might not be necessary.

Surgeries and other procedures

Your child will likely need several surgical procedures to treat hypoplastic left heart syndrome. Surgeons perform these procedures to create separate pathways to get oxygen-rich blood to the body and oxygen-poor blood to the lungs. The procedures are done in three stages.

  • Norwood procedure. This surgery is usually done within the first two weeks of your child's life. There are several ways to do this procedure.

Surgeons reconstruct the aorta and connect it to the heart's lower right chamber (right ventricle). Surgeons insert a tube (shunt) that connects the aorta to the arteries leading to the lungs (pulmonary arteries), or they place a shunt that connects the right ventricle to the pulmonary arteries. This method allows the right ventricle to pump blood to both the lungs and the body.

In some cases, a hybrid procedure is done. Surgeons implant a stent in the ductus arteriosus to maintain the opening between the pulmonary artery and aorta. Bands placed around the pulmonary arteries reduce blood flow to the lungs and create an opening between the atria of the heart.

After the Norwood procedure, your baby's skin will still have a blue coloring because oxygen-rich and oxygen-poor blood continue to mix within the heart. Once your baby successfully passes through this stage of treatment, the odds of survival can increase.

  • Bidirectional Glenn procedure. This procedure is generally the second surgery. It's done when your child is between 3 and 6 months of age. Doctors remove the first shunt attached to the pulmonary arteries, and then connect one of the large veins that normally returns blood to the heart (the superior vena cava) to the pulmonary artery instead. If surgeons previously performed a hybrid procedure, they'll follow additional steps during this procedure.

This procedure reduces the work of the right ventricle by allowing it to pump blood mainly to the aorta. It also allows most of the oxygen-poor blood returning from the body to flow directly into the lungs without a pump.

After this procedure, all the blood returning from the upper body is sent to the lungs, so blood with more oxygen is pumped to the aorta to supply organs and tissues throughout the body.

  • Fontan procedure. This surgery is usually done when your child is between 18 months and 4 years of age. The surgeon creates a path for the oxygen-poor blood in one of the blood vessels that returns blood to the heart (the inferior vena cava) to flow directly into the pulmonary arteries. The pulmonary arteries then transport the blood into the lungs.

The Fontan procedure allows the rest of the oxygen-poor blood returning from the body to flow to the lungs. After this procedure, there's minimal mixing of oxygen-rich and oxygen-poor blood in the heart, and your child's skin will no longer look blue.

  • Heart transplant. Another surgical option is a heart transplant. However, the availability of a heart to be used for transplant is limited, so this option is not used as often. After a heart transplant, your child will need medications throughout life to prevent rejection of the donor heart.

Follow-up care

After surgery or a transplant, your baby will need lifelong follow-up care with a cardiologist trained in congenital heart diseases. Some medications might be needed to regulate heart function. Various complications can occur over time and might require further treatment or other medications.

Your child's cardiologist will tell you whether your child needs to take preventive antibiotics before certain dental or other procedures to prevent infections. In some cases, the doctor might also recommend that your child limit physical activity.

Follow-up care for adults

As an adult, you'll transition from a paediatric cardiologist to a cardiologist trained in congenital heart disease in adults. Only recently have advances in surgical care resulted in children with hypoplastic left heart syndrome surviving into adulthood, so it's not yet clear the challenges an adult with the condition might face. You'll need regular, lifelong follow-up care to monitor for any changes in your condition.

Women considering pregnancy should discuss pregnancy risks and birth control options with their doctors. Having this condition increases your risk of cardiovascular problems during pregnancy, the risk of miscarriage and the risk of having a baby with congenital heart disease.