Hypoplastic Left Heart Syndrome (HLHS)

Nemours Cardiac Center at Nemours/Alfred I. duPont Hospital for Children

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Children’s heart conditions can’t be prevented, but a lot can be done to improve and often completely repair their hearts at any age. Thanks to advanced technology and the pediatric heart experts at the Nemours Cardiac Center (based at Nemours/Alfred I. duPont Hospital for Children), most children born with a heart problem — even newborns only hours or days old — can be quickly diagnosed and treated right when it matters the most. At the Cardiac Center, we specialize in early detection and repair of congenital heart defects (also often called, “congenital heart disease”).

If your child’s been diagnosed with hypoplastic left heart syndrome (or “HLHS,” for short), we’re here to ease your concerns, answer your questions, and give your child the best possible chance for a healthy future.

What Is It?

Normally, both the right and left side of the heart are similar in size and able to pump the same amount of blood. But sometimes, during an unborn baby’s development in the womb (during pregnancy), there’s underdevelopment of one side of the heart or the other. When the left side of the heart is underdeveloped, it’s called “hypoplastic left heart syndrome.” “Hypoplasia” means underdevelopment of a tissue or organ. The “left heart,” in this context, means all the portions of the heart that receive blood from the lungs and pump them out to the body, including the:

  • left atrium (the upper left-hand chamber of the heart that receives oxygen-rich red blood from the lungs, and then sends this blood to the left ventricle)
  • left ventricle (the lower left-hand chamber of the heart that receives oxygen-rich red blood from the left atrium and pumps it into the aorta, which takes the blood to the body)
  • mitral valve (the valve between the left atrium and left ventricle that consists of two flaps, or “cusps,” and prevents blood from flowing back into the atrium from the ventricle)
  • aortic valve (the valve that regulates blood flow from the left ventricle into the aorta which consists of three flaps and prevents blood from flowing back into the ventricle)
  • aorta (the blood vessel that delivers oxygen-rich blood from the left ventricle to the body)

In children with hypoplastic left heart syndrome, oxygen-rich (“red”) blood returns from the lungs just like in any other baby. However, the hypoplastic left ventricle is too small to accept this blood and pump it out to the body. Instead, most of this blood will flow through a hole between the top two chambers called an “atrial septal defect” (or “ASD”) from the left to the right atrium. This blood mixes with the oxygen-poor (“blue”) blood returning from the body and enters the right ventricle.

As the only pumping chamber, the right ventricle must then pump this blood mixture through the pulmonary artery (the large artery that normally receives blood from the right ventricle and carries it to the lungs) with some of the blood going to the lungs and the rest will reach the aorta through a patent ductus arteriosus (or “PDA”), which is a large blood vessel connecting the pulmonary artery and aorta.

Although the PDA is necessary while a baby remains in the womb, it usually closes within the first few days after birth. But in children with hypoplastic left heart syndrome, it’s critical that the PDA remains open, as this is the only way blood is able to get out to the body. To prevent the PDA from closing, babies have to receive intravenous (IV) medication.

How Does the Heart Normally Work?

When your child has a congenital heart defect, there’s usually something wrong with the structure of the heart. In order to understand your child’s condition, it can help to know how the heart should work normally.
Learn More About Normal Cardiac Anatomy »

Nemours’ experts at KidsHealth.org also offer these helpful resources to help both you and your child understand how the heart works:

How & When Is It Diagnosed?

These days, hypoplastic left heart syndrome is usually diagnosed by a fetal echocardiogram (“echo”) during pregnancy. When babies who haven’t been previously diagnosed are born with HLHS, they may get sick very rapidly with both:

  • hypoxia (low levels of oxygen in the blood, which makes the skin look blue — this is called “cyanosis”)
  • poor blood flow to the body
How & When Is It Treated?

Hypoplastic left heart syndrome requires surgical treatment in all cases. As long as the patent ductus arteriosus remains open, babies are usually stable for the first few days. However, as the resistance to blood flow through the lungs (called the “pulmonary vascular resistance”) drops in the first days after birth, more and more blood will be pumped to the lungs and less and less to the body, which progressively causes heart failure.

Some babies with HLHS don’t have an intact atrial septum and are very sick at birth because the blood can’t easily get out of the lungs. These babies often need emergency procedures immediately after birth. At the Nemours Cardiac Center, we’re equipped and experienced in handling babies within the first few minutes after birth.

Initial options for the treatment of hypoplastic left heart syndrome include heart transplantation or an operation known as the “Norwood procedure.” Although heart transplantation was popular as an initial treatment for hypoplastic left heart syndrome, wait times are very long, and this isn’t typically considered the best for newborns with HLHS.

The Norwood Procedure (“First-Stage Palliation”)

As an alternative to heart transplantation, the Norwood procedure was pioneered by the Nemours Cardiac Center’s founder, Dr. William Norwood, and is now used worldwide to treat hypoplastic left heart syndrome.

The goal of the Norwood procedure is to enlarge the aorta and use the right side of the heart to replace the function usually performed by the left. This way, oxygen-rich blood from the lungs flows through the right heart (bypassing the hypoplastic left heart), mixes with the oxygen-poor blood from the body, and is pumped out the pulmonary artery, which has been connected to the aorta and then out to the body. Following the Norwood procedure, children need at least two more operations to complete the process of a series of operations called “single ventricle palliation.”

“Palliation” is the term used when a surgical procedure creates an alternative circulation, rather than repairing the heart and returning it to a “normal” circulation. Palliative procedures are usually performed when a complete repair isn’t possible, usually because certain structures of the heart are too small or completely absent.

The Norwood procedure is often called a “stage 1 Norwood procedure” because it’s the first stage of three procedures required for complete palliation. Since Dr. Norwood developed the procedure named after him, it has been modified and variations have been developed, which may be useful in certain children.

The various options include:

Stage I Norwood procedure. Our Nemours Cardiac Center surgeons usually perform this operation in the first week or two after birth. To create a new, larger aorta, the connection between the right ventricle and the branch pulmonary arteries is broken and the main pulmonary artery (the large artery that receives blood from the right ventricle and carries it to the lungs) and the small aorta (the blood vessel that delivers oxygen-rich blood from the left ventricle to the body) are connected and enlarged. Next, a small tube (called a “modified Blalock-Taussig” or “B-T shunt”) is placed between a branch of the aorta and the right branch pulmonary artery to allow for blood flow to the lungs. This way, both oxygen-rich “red” blood from the lungs and oxygen-poor “blue” blood from the body mix within the right ventricle and are pumped out the pulmonary artery and into the augmented aorta. Some of that blood then travels through the shunt to the lungs to pick up more oxygen. 

Modified stage 1 Norwood procedure with a right ventricular to pulmonary artery conduit. In certain cases, instead of the modified B-T shunt, children may benefit from a modified stage 1 Norwood procedure with a right ventricular to pulmonary artery conduit. In this procedure, a heart surgeon sews in a tube to connect the right ventricle back to the pulmonary artery branches. The “red” and “blue” blood mix in the right ventricle, and then the mixed blood is simultaneously pumped out to both the body (through the pulmonary artery now connected to the augmented aorta) and to the lungs (through the right ventricular to pulmonary artery conduit).

Hybrid Norwood procedure. This consists of combining a surgical procedure with a catheter procedure. When these two types of procedures are combined, we call it a “hybrid” procedure. Instead of controlling blood flow to the lungs by using a small shunt or conduit, in a hybrid procedure, blood flow to the lungs is controlled by tightening the branch pulmonary arteries using rings or “bands.” Next, instead of disconnecting the pulmonary artery and then reconnecting it to the aorta, blood is delivered to the body through the patent ductus arteriosus, which is kept open either through intravenous medicine or by placing a tiny metal cage into the vessel (called a “stent”) which functions like scaffolding to keep the ductus arteriosus open.

This hybrid procedure is used in specific circumstances, especially when a newborn baby hasn’t been diagnosed early and comes in for surgery very sick. Following the hybrid procedure, we still need to perform surgery, which may consist of the stage 1 Norwood procedure. Sometimes, though, surgery may be delayed three to four months and the stage I (Norwood) procedure and stage II are combined into one large procedure, called a “comprehensive stage 2.”

Which of these options is best in any individual child depends on a combination of factors, including the exact size of the various parts of the left heart and the condition in which the baby arrives in the hospital. In all cases, these are very complicated operations.

Surgical Treatment After the Norwood Procedure

Following the 1st stage palliation, children must undergo at least two additional operations:

  • the Second Stage (either a “hemi-Fontan” operation or a “bidirectional Glenn” procedure)
  • the Third Stage (called the “Fontan procedure”)

Learn More
How Will It Affect My Child Long Term?

There’s a lot of variability in how children can function after these surgical procedures. Some participate in sports and seem like any other child with a normal two-ventricle heart. Others may struggle with late complications or have trouble exercising at the same level as their peers. Some of this depends on the function of both the heart and its valves.

Nevertheless, 30 years ago (before the pioneering work of Dr. Norwood) no baby with a diagnosis of hypoplastic left heart syndrome lived past a year old. Now, children with HLHS routinely live into and through adulthood.

If your child has hypoplastic left heart syndrome, know that at the Nemours Cardiac Center we’re here to give your child the very best, most comprehensive and compassionate care. Our goal is to guide your family, from start to finish, through your child’s heart defect journey — and to help your child live the healthiest, most fulfilling life possible.

Learn More About Congenital Heart Defects »

Why Choose Us

From our outcomes to our family-centered care, find out all of the reasons why your child’s heart will be in good hands at the Nemours Cardiac Center. Learn More »

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Information for Patients

Outpatient Services and Inpatient Units: (302) 651-6660

After 5 p.m. and Weekends:

Cardiac Intensive Care Unit: (302) 651-6644
General Inpatient Unit, 2B: (302) 651-6690


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Hyoplastic Left Heart Syndrome Stories

Meet a couple of our inspiring Nemours Cardiac Center patients who know what it’s like to have HLHS: