What Is Hypoplastic Left Heart Syndrome (HLHS)?

Hypoplastic left heart syndrome (HLHS) is a rare birth defect of a baby's heart. The left side of the heart doesn't grow as it should, making it smaller and weaker than normal.

The left side of the heart is supposed to pump blood out to the body. But a baby's heart with HLHS can't do the job. This makes a baby very sick. Without medicines and a series of three surgeries to rebuild the heart, babies with HLHS won't survive.

The left side of the heart can't be fixed, so the goal of the surgeries is to rebuild parts of the heart and "redirect" the way blood flows to and from the body.

Soon after birth, a baby with HLHS needs around-the-clock care in a hospital for the first weeks or months of life.

How Does the Heart Work?

The heart is a muscle that pumps blood. It acts like two pumps in one. The pumps are called ventricles and each has an important job:

  • The right ventricle gets blood from the body and pumps it out the pulmonary artery to the lungs.

    In the lungs, blood fills up with oxygen and gets rid of carbon dioxide.
  • The left ventricle gets the blood from the lungs and pumps it out through the aorta to the body.

    Because it pumps blood to the entire body, the left ventricle is a stronger pump than the right ventricle.

Illustration: How the heart pumps blood

What Happens in Hypoplastic Left Heart Syndrome?

With hypoplastic left heart syndrome:

  • The left ventricle and aorta are too small to pump enough blood to the body.
  • The right ventricle, which is only supposed to pump blood to the lungs, pumps blood to the lungs and the body through an extra pathway called a patent ductus arteriosis (PDA). That means the right ventricle gets overworked.Illustration: Babies with HLHS rely on two important pathways, an ASD and a PDA.
  • Babies with HLHS are almost always born with an atrial septal defect (ASD). This is a hole in the upper part of the heart. It lets blood with oxygen mix with blood low on oxygen. Then the right ventricle pumps the blood to the lungs and the body.

Illustration: How a heart with HLHS pumps blood

What Are the Signs & Symptoms of Hypoplastic Left Heart Syndrome?

Within a few hours to a day or so after birth, a newborn with undiagnosed HLHS may have:

  • trouble breathing
  • blue or grayish coloring of the skin and nails
  • difficulty feeding
  • lethargy (very little activity)
  • weak pulses in the arms and legs
  • few wet diapers

What Causes Hypoplastic Left Heart Syndrome?

HLHS is a birth defect that happens when a baby is growing in the womb. No one knows exactly what causes it, but it could have a mix of causes, including a baby's genes (DNA).

How Is Hypoplastic Left Heart Syndrome Diagnosed?

Hypoplastic left heart syndrome can be diagnosed with:

How Is Hypoplastic Left Heart Syndrome Treated?

HLHS is first treated with medicines, and then a series of three surgeries. Without surgery, a baby won't survive. Treatment for HLHS starts as soon as the baby is born.


Immediate treatment includes a medicine called prostaglandin. Prostaglandin keeps the PDA open so oxygen can get to the body.

Some babies need other medicines to help balance how much blood goes to the lungs and how much goes to the body.

Also if the ASD is too small, it might be made bigger. This is done with a cardiac catheterization procedure or by surgery.

The Surgeries

Because the left ventricle and aorta are too small, the goals of the surgeries are to:

  • Use the right ventricle to pump oxygen to the body.
  • Send the blood coming back from the body straight to the lungs without having to pass through the heart.

Surgeries are done in stages as a baby grows. They are (in order):

  1. Norwood Procedure
  2. Glenn Procedure
  3. Fontan Procedure

Looking Ahead

Being actively involved in your child's care plan can help you feel more in control.

  • Take things one day at a time.
  • Look to your care team to guide you on caring for your child, getting ready for surgery, recovery, and more. If you have questions, ask.
  • Learn from others. Find a support group for families dealing with a heart problem or talk to other parents whose kids have had heart surgery. Support groups include:
  • Accept help when you can, and lean on those around you for support.
  • Keep a journal to record your questions for the medical team.
  • Partner with your care team to face the challenges ahead.
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Note: All information is for educational purposes only. For specific medical advice, diagnoses, and treatment, consult your doctor. © 1995-2021 KidsHealth®. All rights reserved. Images provided by The Nemours Foundation, iStock, Getty Images, Veer, Shutterstock, and Clipart.com.