Hypoplastic Left Heart Syndrome (HLHS)

Q: What is HLHS?


Hypoplastic left heart syndrome (HLHS) is one of the most challenging and complex congenital heart diseases to care for. Without treatment, this defect is usually fatal within the first weeks of life. The Children's Heart Program is expert in diagnosing and surgically treating the hearts of babies born with HLHS so that they can live longer lives.

HLHS is a congenital heart defect in which the left side of the heart is small or hypoplastic. The left ventricle, mitral valve, aortic valve, and aorta are all under-developed, and the left side of the heart is unable to send enough blood with oxygen to the body. This results in the left side of the heart being unable to support the circulation needed by the body's organs.

The condition is congenital (present at birth) and is more common in males than in females.

Learn about the University of Maryland's stem cell clinical trial to treat patients with HLHS.

Q: What causes HLHS?


There is no known cause of HLHS. Approximately 10% of patients with HLHS also have other birth defects, and some have genetic disorders. HLHS is more common in families where another family member has HLHS, or other congenital heart defects like aortic stenosis or coarctation of the aorta.


Q: How is HLHS diagnosed?


HLHS is often diagnosed by fetal ultrasound before the baby is born. Sometimes HLHS is not detected before birth. Those babies may initially appear healthy, although their oxygen levels will be slightly decreased. They may develop difficulty breathing, fast breathing, poor feeding, or cool and pale extremities. If HLHS or another heart defect is suspected, the baby will be evaluated by a pediatric cardiologist. That evaluation would include measuring the oxygen level, an electrocardiogram (ECG), and an echocardiogram (ultrasound of the heart). The echocardiogram would show the abnormal structure of the heart.

Q: Why does HLHS make babies sick?


The left side of the heart is normally responsible for receiving blood rich oxygen from the lungs and pumping that blood out to the body. In HLHS, the blood that returns from the lungs comes into the left atrium (or collecting chamber), but little or no blood can get into the left ventricle and out to the aorta. This means that there is no way to deliver oxygen and nutrients to the body. Instead, the blood from the left atrium crosses through a hole in the wall separating the left and right atrium (called a PFO) and mixes with the oxygen poor blood that is returning from the body. That mixture of blood will get pumped out to the lungs by the right ventricle.

Before birth and for a short time after birth, babies are able to use other routes to get blood to the body. A connection between the pulmonary artery (artery from the right ventricle to the lungs) and the aorta allows the right ventricle to pump some of the blood out to the aorta. That connection, called a patent ductus arteriosus (PDA), is present in everyone before birth and closes within the first week of life. It is when that PDA closes that babies with HLHS get very sick.

Q: How is HLHS treated?


The immediate treatment for newborns with HLHS is to ensure that the blood returning from the lungs has a way to get to the body. Babies are started on an IV medication called prostaglandins to keep the PDA open. This allows the right ventricle to be the pump to both the lungs and the body. Some babies may also need a procedure to enlarge the PFO to make sure that the blood returning from the lungs to the left atrium can easily pass into the right side of the heart.

These treatments help to stabilize the baby for surgery, but don't provide a long term solution. We don't yet have a way to make the left side of the heart normal, but there is a series of surgeries that allows us to use one ventricle as a pump and still get blood to both the body and lungs. 

Patients with HLHS undergo three palliative surgeries: 


The first surgery happens in the first week or so of life. The procedure is called the Norwood operation.

The Norwood operation is an open heart surgery that accomplishes three goals: getting blood to the lungs, getting blood to the body, and making sure that the blood returning from the lungs can get to the right side of the heart. The surgeon attaches the pulmonary artery and the aorta to create one large blood vessel that goes from the right ventricle to the body. This means that the branches of the pulmonary artery that go out into the lungs are no longer attached to the heart. A tube is placed that connects either the right ventricle or the aorta to the pulmonary artery branches and creates a stable way to get blood to the lungs. Finally, the wall between the right and left atria is cut out to allow all the blood coming back from the lungs to get to the right side of the heart.

The Norwood procedure accomplishes the three goals but is not a final solution. The right ventricle has to do extra work, by pumping blood to both the lungs and the body, and the body gets blood that is a mixture of oxygen rich and oxygen poor blood. Also, the tube that gets blood to the lungs will not grow with the baby.

Glenn Shunt

When babies are 4 to 6 months of age, a second procedure is done. This is called a Glenn shunt, and it is the first step of separating the lung and body circulations. The large vein that drains the oxygen poor blood from the head and upper body into the right atrium (called the superior vena cava, or SVC) is detached from the heart and attached directly to the pulmonary arteries. This lets the blood drain directly into the lungs. The tube connecting the right ventricle or aorta to the pulmonary artery is removed. After this procedure, the right ventricle only has to pump the blood to the body, so it doesn't have to work as hard. However, all of the oxygen poor blood from the lower body is still coming into the right atrium by another large vein (called the inferior vena cava, or IVC) and mixing with the blood from the lungs. This means that the blood going to the body still has a decreased oxygen level.


The final procedure, called the Fontan operation, takes care of this problem and is usually done around 2 to 4 years of age. In this surgery, the IVC is removed from the heart and connected to the pulmonary arteries. At this point, all of the oxygen poor blood will drain directly into the lungs, and the right ventricle will pump oxygen rich blood to the body.


View our pediatric cardiac surgery outcomes.

Q: What is the long term outcome for children with HLHS?


Survival for infants with HLHS has been improving as we have improved our techniques and approaches to the management of this complicated disease. Surgery for HLHS was only first performed a few decades ago. There are now adolescents and young adults with HLHS who had successful surgeries when they were infants. Patients with HLHS may need to take medications and may have some limitations in their exercise ability. Despite this, they are often able to lead happy and productive lives. As we develop new technologies and ways of approaching this disease, we expect that infants born today with HLHS will have even better outcomes.

Children with HLHS will need lifelong follow-up with a cardiologist. Follow-up visits are frequent when they are young. After they have completed the series of surgeries, they will be seen every 6 to 12 months. At follow-up visits, children will get regular ECGs and echocardiograms. Other tests, such as cardiac MRIs, exercise stress tests or Holter (24 hour ECG) monitors may be also be performed.