Hypoplastic Left or Right Heart Syndrome (HLHS)

Anatomy of the heart, normal

Hypoplastic left heart syndrome (HLHS) is a combination of several abnormalities of the heart and great blood vessels. It is a congenital (present at birth) syndrome, meaning that the heart defects occur due to underdevelopment of sections of the fetal heart beginning during the first eight weeks of pregnancy.

In the normal heart, oxygen-poor (blue) blood returns to the right atrium from the body, travels to the right ventricle, then is pumped through the pulmonary artery into the lungs where it receives oxygen. Oxygen-rich (red) blood returns to the left atrium from the lungs, passes into the left ventricle, and then is pumped out to the body through the aorta.

In hypoplastic left heart syndrome, most of the structures on the left side of the heart are small and underdeveloped. The degree of underdevelopment differs from child to child. The structures affected usually include the following:

  • Mitral valve. The valve that controls blood flow between the left atrium and left ventricle in the heart.

  • Left ventricle. The lower left-hand chamber of the heart. It receives oxygen-rich (red) blood from the left atrium and pumps it into the aorta, which takes the blood to the body. The left ventricle must be strong and muscular in order to pump enough blood to the body to meet its requirements.

  • Aortic valve. The valve that regulates blood flow from the heart into the aorta.

  • Aorta. The largest artery in the body and the primary blood vessel leading from the heart to the body.

Anatomy of a heart with hypoplastic left heart syndrome

Perhaps the most critical defect in HLHS is the small, underdeveloped left ventricle. This chamber is normally very strong and muscular so it can pump blood to the body. When the chamber is small and poorly developed, it will not function effectively and cannot provide enough blood flow to meet the body's needs. For this reason, an infant with hypoplastic left heart syndrome will not live long without surgical intervention:

  • Hypoplastic left heart syndrome occurs in 2 to 3 out of every 10,000 live births or 1 in every 4,344 babies born in the U.S. each year. 

  • HLHS occurs slightly more often in boys than in girls.

Prevention & Risk Treatment

Prevention & Risk Treatment

What causes hypoplastic left heart syndrome?

Some congenital heart defects may have a genetic link, either occurring due to a defect in a gene, a chromosome abnormality, or environmental exposure, causing heart problems to occur more often in certain families. In hypoplastic left heart syndrome, there may be abnormalities of other organs, such as diaphragmatic hernia, omphalocele, and hypospadias.

In many children, HLHS occurs sporadically (by chance), with no clear reason for their development.

What are the symptoms of hypoplastic left heart syndrome?

Infants with HLHS usually develop symptoms shortly after birth. The following are the most common symptoms of hypoplastic left heart syndrome. However, each child may experience symptoms differently. Symptoms may include:

  • Cyanosis (blue color of the skin, lips, and nail beds)
  • Pale skin
  • Sweaty or clammy skin
  • Cool skin
  • Heavy and/or rapid breathing
  • Fast heart rate
  • Cold feet, diminished pulses in the feet

The symptoms of hypoplastic left heart syndrome may resemble other medical conditions and heart problems. Always consult your child's doctor for a diagnosis.

Diagnosis

Diagnosis

How is hypoplastic left heart syndrome diagnosed?

In many cases, hypoplastic left heart syndrome is diagnosed prenatally. After birth, you or your doctor may have noticed that your baby is listless, breathing rapidly, or cyanotic (blue).

A pediatric cardiologist specializes in the diagnosis and medical management of congenital heart defects, as well as heart problems that may develop later in childhood. The cardiologist will perform a physical examination, listening to the heart and lungs, and make other observations that help in the diagnosis. Diagnostic testing for congenital heart disease varies by the child's age, clinical condition, and institutional preferences. Some tests that may be recommended include the following:

  • Chest X-ray. A diagnostic test that uses invisible X-ray energy beams to produce images of internal tissues, bones, and organs onto film.
  • Electrocardiogram (ECG or EKG). A test that records the electrical activity of the heart, shows abnormal rhythms (arrhythmias or dysrhythmias), and detects heart muscle damage.
  • Echocardiogram (echo). A procedure that evaluates the structure and function of the heart by using sound waves recorded on an electronic sensor that produce a moving picture of the heart and heart valves. All patients with HLHS are diagnosed by echocardiography.
Children's Team

Children's Team

Providers

Our Stories

Our Stories

Ryan's Story

Ryan was born with a rare condition -- his heart developed outside his body. Find out how Children's doctors worked together to help Ryan thrive.

Caelen's Story

Our son Caelen was diagnosed in utero at 19 weeks. At first we thought, "why us?" As our pregnancy progressed, we began to think, "why not us," and started learning as much as we could.

Maren's Story

"Randy and I knew Children's was the best choice for Maren and us as a family. I never had to beat myself up, wondering if we had made the right choice. It was already settled in my mind that the best choice was made."

Patient story

Addison's Story

"If you are reading this because your child has been diagnosed with hypoplastic left heart syndrome, just know that you are in good hands at Children's."

Ian's Story

Ian was born with a heart that was not fully formed, the specialists at Children's National rebuilt his heart to function normally and gave him all the energy he'll ever need.

Patient story

Athena's Story

"To all the parents out there with a baby with hypoplastic left heart, good days will come. These babies overcome what seems impossible and have so much love to offer."

Janaya's Story

"The one thing that helps is to talk about what you are feeling, cry if you need to, always be involved in your child's care, and ask questions if you don't understand."

Departments

Departments

Fetal Heart Program

When your baby needs the most advanced cardiac care, Children’s National Heart Institute is the preeminent provider of fetal cardiac services in the Washington, DC, metropolitan area.

Cardiac Surgery

Learn more about the comprehensive, expert care we provide for infants and children in our heart surgery program.

Cardiology

Children’s National Heart Institute, an international leader in comprehensive cardiac care for infants, children, and adults.

Cardiac Imaging

Learn more about the advanced cardiac imaging procedures we use to diagnose infants and children in our Heart Institute.

Invest in future cures for some of life's most devastating diseases

See other ways to give

Keep in touch with Children's National by signing up for our newsletters.

Sign up now

Alex's Story

Patient story

"He is proud of his scar. He likes to tell people he is special and when they ask him why, he will tell them he had a bad heart and the doctors at Children's National made it all better."

Read More of Alex's Story