Hypoplastic Left Heart Syndrome is a congenital heart condition (a problem that a baby is born with). Below is a description of the heart condition and possible treatments offered.



It is made up of a collection of problems on the left side of the heart. Usually, the pumping chamber (left ventricle) is small (hypoplastic) and the mitral and/or the aortic valve may be narrow, blocked or not formed at all. The body artery (aorta) is often small (hypoplastic) and there is a hole (atrial septal defect) between the two collecting chambers.

The blood’s journey through the heart is very different from normal. The blue (deoxygenated) blood flows into the right collecting chamber (right atrium), through the valve (tricuspid valve) into the right pumping chamber (right ventricle). From there it is pumped up to the lungs where the blood receives oxygen. The red oxygen-filled blood then flows from the lungs into the collecting chamber (left atrium) in the left side of the heart, but it will be unable to then pass into the left pumping chamber (left ventricle). As the valve will be blocked, it therefore passes through the hole between the two collecting chambers into the right side, where it mixes with the blue blood and follows the normal path to the lungs.

Whilst the ductus arteriosus is still open (patent), the blood will pass from the lung artery into the body artery and then around the body. When the duct closes, the baby will no longer have oxygen flowing to their body. Gradually, without medical intervention, the baby would become sicker and die.

Hypoplastic Left Heart Syndrome is a fairly rare problem that occurs in approximately 1 in 5,000 babies and accounts for 1% of all congenital heart disorders.


Modified Norwood Procedure (Stage One)



This is normally performed within a few days of birth or diagnosis of Hypoplastic Left Heart Syndrome, while the ductus arteriosus (connection which joins the lung artery and the body artery) is being kept open with Prostaglandin therapy. (See fetal circulation).

The aims of the first operation are:

  • To improve the flow of red blood (oxygenated blood) around the body by attaching the base (trunk) of the lung artery (pulmonary artery) to the body artery (aorta). It may be necessary to enlarge the body artery with a patch.
  • To provide a blood flow to the lungs through a passage (shunt), creating a link between the lung artery (pulmonary artery) and the body artery (aorta). The passage is made out of soft plastic (Gore-Tex).
  • To create a permanent passage (septectomy) between the collecting chambers (left and right atrium) ensuring that a mix of red (oxygenated) blood and blue (deoxygenated) blood is flowing around the body.
  • This operation is extremely complicated and holds a high risk (chance of the baby dying). Ask your surgeon about the risk for your child. The baby may need to be in hospital for some weeks following this surgery to ensure that their condition is stable before being sent home.

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Modified Norwood Procedure (Norwood with a Sano Shunt)



The reconstruction of the main artery leaving the right side of the heart (pulmonary / aorta vessel) remains as described on the previous page; this provides a flow of blood to the body.

The lung (pulmonary) flow of blood is provided by a Gore-Tex tube that leads from the right pumping chamber (right ventricle) to the left lung vessel (pulmonary artery). This connection ensures that blood reaches the lungs where it collects oxygen that is then passed around the body.

This, like the previously described procedure, is an extremely complicated operation and holds a high risk (chance of the baby dying). Ask your surgeon about the risks for your child.

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Cavo-Pulmonary Connection (Stage Two) for all single ventricle conditions

Bi-directional Cavo-Pulmonary Shunt (Glenn Shunt) or The Hemi-Fontan Operation




As the children grow, they will require a more permanent supply of blood to their lungs than earlier surgical procedures can provide. A Cavo-Pulmonary Connection is normally performed between three and twelve months of age.

The aim of this operation is to redirect the flow of blue blood (deoxygenated blood) to the lungs by attaching the upper body vein (superior vena cava) directly on to the lung artery (pulmonary artery). The Gore-Tex shunt or band that was inserted at the last operation will be taken away.

In some centres the stump of the lower body vein (inferior vena cava) is attached to the base of the lung artery (pulmonary artery). This is known as the Hemi-Fontan operation. Although blood does not flow through this attachment at this time, it prepares the child for the completion of a Fontan procedure at Stage Three.

These operations have fewer risks than the first stage but it is important to talk with the medical team to find out the risks for your child.

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The Fontan Procedure (Stage Three) for all single ventricle conditions or completion of the Cavo-Pulmonary Connection


The final stage of surgery will be performed as the child starts to show that they need more blood flow to the lungs. They may become more breathless on exercise or their growth may slow down. For some children this will occur before they start school. Others may be able to wait a little longer. For more information see the LHM booklet The Fontan.

The Fontan procedure aims to separate the blue (deoxygenated) blood supply and the red (oxygenated) blood supply. Although this does not make the heart function normal, it does allow the children to grow and enjoy more physical activity. The procedure can be performed in two ways.

External Fontan or External Conduit




This operation is done by attaching a tube of a special plastic (a conduit of Gore-Tex) from the lower body vein (inferior vena cava) to the base of the lung artery (pulmonary artery), diverting blue (deoxygenated) blood away from the heart straight to the lungs.

A hole (fenestration) may be created between the tube and the right collecting chamber (right atrium). As with the Internal Fontan (see below) there can be a rise in pressure in the lung arteries after surgery and the hole acts as a pressure valve.

Children may be in hospital for some weeks after the third operation as it is important to give them time to adjust to their new circulation.

Internal Fontan




This is done by creating a wall (baffle) in the right collecting chamber (right atrium) and then attaching the chamber to the base of the lung artery (pulmonary artery). This may have been partially completed at stage two, the Hemi-Fontan.

All the returning blue (deoxygenated) blood will now be flowing to the lungs, without a pump behind it. This causes an increase in pressure within the lung blood vessels, so, to aid circulation, a small hole (fenestration) may be created in the wall (baffle). This acts as a pressure release valve whilst the child’s body adjusts to the new circulation.

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The Hybrid Procedure



In the past many newborn babies were not suitable for the Norwood Procedure for Hypoplastic Left Heart Syndrome because they were too small or too sick. Medical teams have been working to develop a procedure that will support a newborn baby’s heart until he or she is big enough to undergo more complex reconstructive operations. This procedure is called the Hybrid Procedure.

For some babies born with a diagnosis of Hypoplastic Left Heart Syndrome, the Norwood Procedure, the first stage of surgery, may not be possible or may have an exceptionally high risk.

The Hybrid Procedure has been developed as a way to help a baby survive until it is strong enough and big enough for the more complex Norwood Procedure.

The aim of the Hybrid Procedure is to allow flow of oxygen-filled red blood (oxygenated blood) to reach the body and to allow used blue blood (deoxygenated blood) to reach the lungs where it can collect oxygen again.

This is done by keeping open the arterial duct and holes that are in the heart whilst the baby is still inside the womb (fetal circulation), at the same time protecting the lung blood vessels so that they can still be used in later surgery. (See fetal circulation).

The Hybrid Procedure is performed under a general anaesthetic within the cardiac catheter suite or the operating room or possibly both.

The procedure is performed by both a cardiac surgeon and a cardiologist.

There are three parts to this procedure:

  1. Small bands are tightened around the left and right lung arteries (pulmonary arteries) to control the flow of blood and pressure in the lungs.
  2. A mesh of fine metal (stent) is placed in the patent ductus arteriosus (between the pulmonary arteries and the aorta) to keep it open.
  3. At the same time the hole between the upper collecting chambers (atria) may be made bigger and permanent (atrial septostomy). This may be delayed for about a week.

This procedure has less initial risk than the original Stage One Norwood Procedure but children undergoing the Hybrid Procedure are usually sicker or smaller so their personal risks may be high.

Children who have undergone the Hybrid Procedure will need a more complex operation at Stage Two that will incorporate the reconstructive surgery of the usual Stage One Norwood Procedure as well as the Stage Two Cavo-Pulmonary Connection.

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The Damus Procedure



Children who are born with only one of the chambers (ventricles) needed to pump blood around their body and who may also have a narrowing of the body artery (aorta) may need to have surgery to aid circulation of blood from the heart to the body.

The base of the lung artery (pulmonary artery trunk) is attached to the base of the body artery (aorta) to ensure that all the blood that enters the one functioning pumping chamber will be directed around the body.

To ensure that blood also reaches the lungs a connection (shunt) is made between the body circulation and the lung artery (pulmonary artery).

Updated: June 2017

Review due: June 2019

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