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Hypoplastic Left Heart Syndrome (HLHS)

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. This makes a baby very sick. To survive, babies with HLHS need medicines and a series of three surgeries to rebuild the heart.

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.

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

What Happens in Hypoplastic Left Heart Syndrome?

With hypoplastic left heart syndrome, the left side of the heart can't do its job. In a heart with HLHS:

  • The left ventricle (the main pump on the left side) doesn't work as it should or doesn't work at all. It's supposed to pump blood to the body but can't. In response, the right ventricle, which is supposed to pump blood only to the lungs, sends blood to the lungs and the body. This makes the right ventricle work harder than it should.
  • Because there's no pumping from the left side, the aorta (the main tube that carries blood from the heart to the body) is thin and weak.

Babies with HLHS also have an atrial septal defect (ASD), which is a hole in the upper part of the heart. The ASD lets blood that's high in oxygen mix with blood that's low in oxygen. So the body gets some oxygen and nutrients, but not enough.

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 may be a mix of causes that include a baby's genes (DNA).

How Is Hypoplastic Left Heart Syndrome Diagnosed?

Hypoplastic left heart syndrome may be seen on a prenatal ultrasound scan. A fetal echocardiogram can give more information and help the delivery team prepare for care after birth.

Tests after the baby is born include:

How Is Hypoplastic Left Heart Syndrome Treated?

HLHS is treated with a series of three surgeries. Treatment starts as soon as the baby is born.

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

All babies are born with a hole in the heart called the patent ductus arteriosis (PDA). Normally, the PDA closes on its own, and doctors repair atrial septal defects. But both of these holes need to stay open in a baby with HLHS. If they close, blood with oxygen is trapped on the left side of the heart, and can't get to the body. Prostaglandin keeps the PDA and the ASD open.


Because the left ventricle doesn't work and can't be fixed, three surgeries are done. They will:

  • Use the right ventricle to pump oxygen to the body.
  • Make blood from the body come back to the pulmonary artery (the main tube to the lungs) without going 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.

  • 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.
  • Take things one day at a time.
  • 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.

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