Hypoplastic left heart syndrome is a rare heart defect present at birth (congenital). In this condition, the left side of the heart is extremely underdeveloped.

If a baby is born with hypoplastic left heart syndrome, the left side of the heart can't pump blood well. Instead, the right side of the heart must pump blood to the lungs and to the rest of the body.

Treatment of hypoplastic left heart syndrome requires medication to prevent closure of the connection (ductus arteriosus) between the right and left sides of the heart. Plus, either surgery or a heart transplant is necessary. Advances in care have improved the outlook for babies born with this condition.


Babies born with hypoplastic left heart syndrome usually are seriously ill soon after birth. Symptoms include:

  • Grayish-blue color of the lips and gums (cyanosis)
  • Rapid, difficult breathing
  • Poor feeding
  • Cold hands and feet
  • Weak pulse
  • Being unusually drowsy or inactive

If the natural connections between the heart's left and right sides (foramen ovale and ductus arteriosus) are allowed to close in the first few days of life in babies with hypoplastic left heart syndrome, they can go into shock and possibly die.

Signs of shock include:

  • Cool, clammy skin that can be pale or lips that can be bluish-gray
  • A weak and rapid pulse
  • Breathing that may be slow and shallow or very rapid
  • Dull eyes that seem to stare

A baby in shock might be conscious or unconscious.

When to see a doctor

Most babies with hypoplastic left heart syndrome are diagnosed either before birth or soon after. However, seek medical help if you notice that your baby has any of the symptoms of the condition.

If you think that your baby is in shock, immediately call 911 or your local emergency number.


Hypoplastic left heart syndrome occurs in the womb when a baby's heart is developing. The cause is unknown. However, having one child with hypoplastic left heart syndrome, increases the risk of having another with a similar condition.

The heart has four chambers, two on the right and two on the left. In doing its basic job — pumping blood through the body — the heart uses its left and right sides for different tasks.

The right side moves blood to the lungs. In the lungs, oxygen enriches the blood, which then moves to the heart's left side. The left side of the heart pumps blood into a large vessel called the aorta, which sends the oxygen-rich blood to the rest of the body.

What happens in hypoplastic left heart syndrome

In hypoplastic left heart syndrome, the left side of the heart can't properly supply blood to the body. That's because the lower left chamber (left ventricle) is too small or isn't there. Also, the valves on the left side of the heart (aortic valve and mitral valve) don't work properly, and the main artery leaving the heart (aorta) is smaller than usual.

After birth, the right side of a baby's heart can pump blood both to the lungs and to the rest of the body through a blood vessel that connects the pulmonary artery directly to the aorta (ductus arteriosus). The oxygen-rich blood returns to the right side of the heart through a natural opening (foramen ovale) between the right chambers of the heart.

When the ductus arteriosus and the foramen ovale close — which they usually do after the first day or two of life — the right side of the heart has no way to pump blood to the body. Babies with hypoplastic left heart syndrome need medication to keep these connections open and keep blood flowing to the body until they have heart surgery.

HLHS: A child's perspective

Todd and Karen Wanek Family Program for Hypoplastic Left Heart Syndrome — Cause to Cure

HLHS. HLHS. Hypo. Plastic. Left heart. Syndrome.

Hypoplastic left heart syndrome.

Whoa, that's a lot of words!

What is HLHS?

HLHS is when you're missing the bottom left of your heart.

The left side of the heart, it doesn't pump blood as well as the right side. Kids who have HLHS, they all have like a big scar, because they had to have open heart surgery.

I got the surgery when I was a baby.

Three open heart surgeries – two when she was just born, and one when she was two.

I just found out I was going to have a sister, and she was just born, but then she had to be rushed to get surgery, so it was kind of hard.

My brother Henry had three surgeries.

I have a scar on my heart.

He has scars on his heart.

I have stitches on my heart. I needed help.

Children with HLHS may require a heart transplant later in life.

The power of teamwork

What makes a strong team is that people will help you feel better.

I have a team. I have doctors. I have nurses.

And they try and help me feel better.

Everybody's working together to help Sophie stay healthy and feel like a normal girl. There's a lot of teams helping a child with HLHS.

What we all really want, I guess, is just a cure for HLHS.

What is hope?

Hope is when you want something to happen.

Hope is when you have confidence in something.

HLHS research is like a lightsaber is to a Jedi Knight. The more research that we put into HLHS, the more lives will be saved, and the more ... closer we can get to developing a cure.

I hope they all — all the kids with HLHS — be really strong and live a long life.

I hope that the doctors find the cure for HLHS. We're all part of the team.

Join us. hlhsblog.mayoclinic.org

Risk factors

People who have a child with hypoplastic left heart syndrome have a higher risk of having another baby with this or a similar condition.

There are no other clear risk factors for hypoplastic left heart syndrome.


With proper treatment, many babies with hypoplastic left heart syndrome survive. But most have complications later, which may include:

  • Tiring easily during sports or other exercise
  • Heart rhythm problems (arrhythmias)
  • Fluid buildup in the lungs, abdomen, legs and feet (edema)
  • Not growing well
  • Developing blood clots that may lead to a pulmonary embolism or stroke
  • Developmental problems related to the brain and nervous system
  • Need for additional heart surgery or a heart transplant


There's no way to prevent hypoplastic left heart syndrome. Before getting pregnant, people with a family history of heart defects or who have a child with a congenital heart defect might want to meet with a genetic counselor and a cardiologist who treats congenital heart defects.

Hypoplastic left heart syndrome care at Mayo Clinic

Aug. 12, 2022

Living with hypoplastic left heart syndrome?

Connect with others like you for support and answers to your questions in the Heart & Blood Health support group on Mayo Clinic Connect, a patient community.

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