Hypoplastic left heart syndrome factsheet


The heart is made up of four chambers, two on the top and two on the bottom.

  • atria – the two top chambers that receive the blood that flows into the heart
  • ventricles – the two bottom chambers that pump the blood back out of the heart.

Hypoplastic left heart syndrome (HLHS) is when the entire left side of the heart does not develop properly. When this happens, the right side of the heart must pump blood into and out of the body. 

This is a lot of work, and the heart cannot do this forever.

HLHS is a congenital heart defect. A congenital heart defect is a difference in how your child’s heart has grown during pregnancy.

 Signs and symptoms

Signs and symptoms of HLHS will be noticeable at birth or will show up several days later.

They can include:

  • cyanosis – when there is a blue or purple tint to lips, skin, and nails
  • difficulty breathing
  • difficulty feeding
  • a very fast heartbeat
  • being very sleepy or not responding to others
  • weak pulse in the arms and legs  
  • a lower number of wet nappies than expected
  • cold hands and feet.


HLHS can be diagnosed during pregnancy using a fetal echocardiogram. The scan is like the regular ultrasounds done during pregnancy and uses sound waves to show a detailed picture of: 

  • your baby’s heart 
  • it’s structure
  • how well it is pumping blood.

Babies who are diagnosed at birth might:

  • look a bit blue
  • have trouble breathing
  • have an abnormal whooshing sound in their heart, known as a murmur.

The paediatrician who checks your baby after they are born will order tests including:

  • chest x-ray - to show the size and shape of your baby’s heart and lungs
  • echocardiogram - an ultrasound that shows internal heart structures
  • electrocardiogram (EKG) – to measure the electrical changes that happen when your baby’s heart beats
  • pulse oximetry screening – a monitor on the foot or hand that tells you how much oxygen is in your baby’s bloodstream. 

When HLHS is diagnosed, your child will see a heart specialist called a cardiologist.


Generally, it is not possible to replace or rebuild parts of the heart that are missing or not working properly.

After your baby is born, they will have their HLHS treated with medication to help the heart work better, and a series of surgeries. Some babies will need a heart transplant.  

Three surgeries will be done over four years to help guide blood flow to the lungs and body. This is called a staged reconstruction.

Norwood procedure (first two weeks of life)

In the Norwood procedure, parts of the heart are reconstructed, and a tube, or shunt, is placed. This helps the right side of the heart pump blood to the body and the lungs. 

This procedure is done to prevent damage to the heart and lungs until the second operation can be done.

There is a higher risk of this operation not working properly compared to when it is used in other heart conditions.

Bidirectional Glenn shunt operation (at 4-6 months)

The Glenn procedure is done between 4 and 6 months old.

In this procedure, the surgeon will replace the old shunt with a new shunt that lets blood flow straight into the lungs. This lowers the strain on the right side of the heart.

Fontan procedure (18 months-4 years old)

In the Fontan procedure, the large vein that carries blood from the lower body is disconnected from the heart. It is then reconnected to the passage that takes blood out of the heart and into the lungs.

This means blood that needs oxygen can go straight to the lungs without passing through the heart. 

After the Fontan procedure, all blood that needs oxygen will travel straight to the lungs without going through the heart.


Risk factors

HLHS and other heart defects can be passed down in families.

You should meet with a genetic counsellor before getting pregnant if you have a:

  • heart defect
  • family history of heart defects
  • child who was born with a heart defect.

A genetic counsellor is a health professional who can give families information about: 

  • different conditions that can be passed down
  • what the effects on their child might be
  • how to manage or treat the condition
  • what support is available.

Expectations after surgery

HLHS is different for every child. Your doctor can talk to you about your child’s condition, the procedures they need, and how likely they are to recover. 

These procedures cannot make the heart “normal”, but aim to help it work as well as possible.

Your child will need to be watched closely between the first and second operations to make sure they are well. This can mean they will spend some time in hospital.

Children who have had these procedures will need ongoing checkups with their doctors to make sure there are no other heart issues, and may need medication to manage symptoms.

Last updated Friday 9th February 2024


This factsheet is provided for general information only. It does not constitute health advice and should not be used to diagnose or treat any health condition.

Please consult with your doctor or other health professional to make sure this information is right for you and/or your child.

The Sydney Children’s Hospitals Network does not accept responsibility for inaccuracies or omissions, the interpretation of the information, or for success or appropriateness of any treatment described in the factsheet.

© Sydney Children’s Hospitals Network 2024