Hypoplastic Left Heart Syndrome (HLHS) | Diagnosis & Treatment

How is hypoplastic left heart syndrome (HLHS) diagnosed before birth?

Most pregnant women have fetal ultrasounds during the course of their pregnancies. If a basic (level one) ultrasound shows the possibility of heart abnormalities, a more detailed cardiac ultrasound — fetal echocardiography — can correctly diagnose your baby’s heart defect. In addition, fetal magnetic resonance imaging (MRI) may provide more information about the heart.

What happens immediately after a baby is born with HLHS?

Most babies with HLHS appear healthy immediately after birth. If your baby was not diagnosed during pregnancy, it will become apparent within the first few hours to days that your baby has a heart defect. Some combination (not necessarily all) of the following medical tests will be used to diagnose or evaluate HLHS and its related defects in a newborn:

Based on the results of the evaluation and the extent of the HLHS, doctors will determine the best treatment approach and the necessary interventions required

What are the treatment options for HLHS?

Fetal cardiac intervention

A small number of babies with hypoplastic left heart syndrome (HLHS) may benefit from intervention before birth. Pediatric interventional cardiologists can use a needle or tiny balloon catheter to treat HLHS, as well as certain other fetal cardiac abnormalities. Balloon catheters can be inflated to open abnormal heart valves or other obstructions. Learn more about the Fetal Cardiology Program.

Before surgery

If fetal intervention is not an option for your baby, initial treatments after birth will focus on stabilizing your baby and may include:

  • medication to keep the patent ductus arteriosus open
  • intravenous fluids through a tube inserted into a vein
  • a feeding tube if your baby has difficulty feeding
  • breathing assistance provided by a ventilator ensuring adequate oxygen delivery
  • a balloon atrial septostomy procedure to create an opening in the wall between the upper chambers of the heart to improve mixing of oxygen-rich blood (red) and oxygen-poor blood (blue)

Shortly after birth, your child’s care team will obtain imaging of your baby’s heart using an echocardiogram to see every detail of your baby’s heart — the way the blood flows, the size and function of the ventricles, and how well the valves work.


To treat HLHS, your child will likely need three operations called the Fontan Sequence. The goal of these surgeries is to enable the fully-functioning right ventricle to do the work normally done by two ventricles and to separate the low-oxygen-content (blue) blood from the well-oxygenated (red) blood.

Stage 1: Norwood procedure (newborn)

The Stage 1 procedure, also known as the Norwood procedure, is one of the most complex surgeries performed. The procedure was developed at Boston Children’s Hospital in 1979 by William Norwood, MD, and first described in the New England Journal of Medicine. Boston Children’s performs approximately 40 Stage 1 procedures each year, and we have a dedicated team of neonatal cardiac surgeons who specialize in this and other neonatal procedures.

The Stage 1 procedure begins with an incision in the front of the chest and exposure of the heart, lungs, and great vessels (pulmonary artery and aorta). The next step will be to place your baby onto heart-lung bypass, a specialized machine which provides blood flow and oxygen to your baby during the operation.

There is a dedicated team of specialists called perfusionists, who along with the rest of the team, make sure that your baby’s brain and other organs get enough oxygen. Bypass takes place through small special tubes, called cannulas, which are placed into the heart to drain blood returning to the heart (so that it is empty and can be opened to perform the operation) give it oxygen, and returns it back into the body.

The next part of the operation includes a reconstruction of the aorta, which had previously only received blood from the ductus arteriosus and any small amount of blood coming through the aortic valve. In this part of the procedure, blood from the right side of the heart is routed into the aorta by connecting the root of the pulmonary artery (now called the neo-aorta) to the aorta (now called the native aorta). The rest of the aorta (which was too small) is then attached to these two vessels and its size significantly expanded using a patch of tissue. This is the most technically challenging and complex part of the operation.

Then, the wall separating the right and left side of the atrium (the atrial septum) is either cut out completely, or in some patients, replaced with a patch that has a hole in it (in patients with a less severely affected left ventricle). Finally, a connection between either the ventricle (Sano shunt) or one of the vessels coming off of the aorta (Blalock–Taussig shunt) is connected to the pulmonary artery (which had been disconnected from the right ventricle) to provide blood flow to the lungs.

Your baby will then be weaned carefully from the bypass machine, and started on medications to help the heart squeeze better. Once the operation is complete, the team will perform a complete echocardiogram to make sure the operation looks as expected. A few additional catheters will be placed into the heart itself for monitoring, a few drains placed into the chest and a dressing placed over the chest. In the majority of cases, the chest will be closed with a small patch will be left open for a few days while your baby recovers.


An alternative to Stage 1: The hybrid procedure

Sometimes, children have certain features that make it quite risky to use heart-lung bypass. For example, a child may be premature, have bleeding in the brain or have severe lung disease. In cases like these, sometimes your care team may consider an alternative to Stage 1 that does not require heart-lung bypass, but that keeps your child safe after birth.  The key features of this procedure include:

  • limiting the amount of blood flow going to each lung by placing a restricting suture or band on each of the pulmonary arteries
  • maintaining a pathway for blood to get from the right ventricle to the aorta through the patent ductus arteriosus using a long-term medication (prostaglandin) infusion or using a stent 

Although this is a technically somewhat less complex approach than Stage 1, there are still drawbacks to it. In most cases, all the Stage 1 steps will still have to take place at a later date — and the future operations become more complicated. Nonetheless, the hybrid approach may allow valuable time for recovery and growth in certain situations.

Stage 2: Bidirectional Glenn procedure (three to six months)

As a result of the Stage 1 procedure, the heart has to work harder. The priority for the next stage is to deliver oxygen to the body more efficiently. During the second surgery, the blue blood that is coming back from the upper body is redirected, so that the blood is channeled directly into the lungs, an operation called the bidirectional Glenn (or superior cavopulmonary connection). This operation involves removal of the previous Sano or BT shunt to the lungs. 

Stage 3: Fontan procedure (two to three years)

Following discharge from the Glenn operation, the vast majority of children do well. The final Stage of the "single ventricle" pathway is called the Fontan operation, a procedure in which blood from the lower half of the body (inferior vena cava) is diverted directly to the lungs. This is accomplished with a tube graft that lies next to the heart (extracardiac) or through a pathway created within the heart (lateral tunnel).

After this procedure, red blood flows from the heart to the body, and then the blue blood returns to the lungs directly to receive oxygen again. This circulation most closely resembles normal, despite only having one pump. 

Biventricular repair

While the most common approach for treating newborns with HLHS is the Fontan sequence, in some cases, steps can be taken to prepare the left side of the heart to function independently, so your baby’s single ventricle heart can be converted into two functioning ventricles (biventricular circulation). This may be an option for children with borderline HLHS. In some situations, this repair can be the initial procedure, but in others, a series of procedures may be used to rehabilitate the small ventricle before converting the heart to biventricular circulation.

Home monitoring between Stages I and II

During the period between Stage I and Stage II surgeries, your baby’s heart circulation requires extra monitoring to prevent complications. The program will give you goals for your baby’s growth and oxygen saturation levels and provide monitoring equipment for your baby. You’ll also get information on when to call. 

What is the long-term outlook for children with HLHS?

The long-term outlook for children with HLHS continues to improve. The ultimate lifespan and quality of life depends on multiple factors. Every year, advancements further extend and improve quality of life. 

Your care team will have an ongoing relationship with your family and can help you create a long-term care program for your baby. The team can also advise you and your child on daily-life issues such as exercise, activity levels and nutrition.