What Is Hypoplastic Left Heart Syndrome?

Medically Reviewed by James Beckerman, MD, FACC on July 20, 2021
4 min read

Sometimes during pregnancy, the left side of a baby's heart doesn't grow the way it should. This causes a rare defect called hypoplastic left heart syndrome (HLHS). About 1,000 babies are born with it in the U.S. each year.

Normally, the right side of your heart pumps blood from your heart to your lungs where it gets oxygen. After it goes back to your heart, the left side then pumps the oxygen-rich blood to the rest of your body.

The heart of a baby with HLHS can't do this. The lower left chamber may be smaller than normal or not there at all. The valves on the left side may not work right or the main artery leaving the heart may not be as big as it should be.

A baby with HLHS also may have a hole between the left and right upper chamber of their heart. This is called an atrial septal defect, and it can cause too much blood to flow to the lungs.

Signs of HLHS may not show up until a few days after birth. For the first day or two, a baby's heart can adjust to the defect. If the left side of the heart can't pump blood very well to the rest of the body, the right side will do more work. But the adjustment only lasts a few days.

A newborn has a blood vessel that connects the two sides of their heart. It's called the patent ductus arteriosus, and it stays open for only a few days after birth. After that, it naturally closes. This is when most babies with the defect start to show symptoms from the lack of oxygen-rich blood and overworked heart.

Doctors don't know why HLHS happens, but it does run in families. Some experts think that what the mother eats, drinks, or comes into contact with during pregnancy may also increase the risk that their baby will have HLHS. This might include smoking or drinking alcohol or not taking a prenatal vitamin with folic acid.

Heart defects can show up on an ultrasound during the second trimester of pregnancy. So some parents find out about it before their babies are born.

In other cases, HLHS is found a few days after the baby's born. The signs include:

  • Being sleepy or not wanting to move
  • Cold hands and feet
  • Fast breathing or difficulty breathing
  • Gray or blue skin
  • Not eating well

When your doctor listens to your baby's heartbeat, they may hear a heart murmur, which sounds like a whooshing noise. This happens because of the unusual blood flow HLHS causes.

If your doctor thinks your baby might have HLHS, they'll order an echocardiogram. This test uses sound waves to make images of their heart on a video screen. It can show the chambers of the heart and track blood flow.

It's important that HLHS is diagnosed and treated right away. If not, your baby's organs won't get enough blood. That can make them go into shock.

Treatments include:

  • Medicine: Your baby may be given a drug called alprostadil (Prostin VR Pediatric) to help keep the ductus arteriosus open. They may also need medicine to make their heart muscle stronger, lower blood pressure, and help their body get rid of extra fluids.
  • Help with feeding and breathing: Your baby will be weak and will likely need to get fluids through an IV or a feeding tube. A breathing machine called a ventilator may also be used to make sure your baby gets enough oxygen.
  • Atrial septostomy. If your baby doesn't have an atrial septal defect, your doctor may recommend this surgery. It creates an opening between the heart's upper chambers to let more blood flow through.

A baby with HLHS also may go through a series of surgeries to help repair their heart. The first, called the Norwood procedure, is done soon after birth. It's a complicated surgery that makes a new aorta for your baby and lets the right ventricle of the heart pump all the blood to the body (after the ductus closes).

Two other surgeries to rebuild the heart and let blood flow the right way usually follow. The timing depends on your child's condition, but the next surgery, known as the Glenn, is usually done when your baby is a few months old. The third surgery is called the Fontan procedure and happens when they are 3 or 4 years old.

In some cases, your doctor may suggest a heart transplant. This will give your child a healthy heart, but it can take time to find a donor. They'll also need to take medicine for the rest of their life so their body doesn't reject it.

Your child will need lifelong care from a heart doctor (cardiologist) who specializes in birth defects. Your child also probably will need more surgery, and there's a good chance that they may have other heart problems, such as irregular heart rhythms and blood clots.

An infant who has surgery to rebuild their heart may grow up physically weaker than other kids and could have some development issues. They may need extra support at home and school.