1 What is Hypoplastic Left Heart Syndrome?

Hypoplastic left heart syndrome is a spectrum of cardiac malformations with normally aligned great arteries without a common atrioventricular junction. It is characterized by underdevelopment of the left heart with significant hypoplasia of the left ventricle including:

  • atresia,
  • stenosis,
  • or hypoplasia of the aortic or mitral valve, or both valves,
  • and hypoplasia of the ascending aorta and aortic arch.

2 Symptoms

Hypoplastic left heart syndrome symptoms include:

  • Grayish-blue skin color (cyanosis)
  • Rapid, difficult breathing
  • Poor feeding
  • Cold hands and feet
  • Being unusually drowsy or inactive

Infants with hypoplastic left heart syndrome can develop life-threatening shock when the ductus arteriosus begins to close. In most cases, however, the ductus arteriosus is widely open at the time of birth, supplying the blood flow to the body, and babies may not be diagnosed right away. As the ductus arteriosus closes, which it typically will in most infants in the first hours or days of life, the perfusion to the body is seriously diminished, and shock rapidly ensues.

Newborns with hypoplastic left heart syndrome will typically have lower-than-normal oxygen saturations. This is because all of the blood from the lungs (the oxygenated "red" blood) mixes together in the single right ventricle before being pumped out of the lungs and body.

Cyanosis, therefore, may be the first clue to the presence of a serious underlying cardiac condition. Respiratory distress (difficult or fast breathing) is often present because the lungs will tend to receive an excessively large amount of blood flow. There is often no or just a faint murmur present in newborns with hypoplastic left heart syndrome.

The pulses may be very weak in all extremities on examination depending on flow through the ductus arteriosus. Lethargy, poor feeding, and worsening respiratory distress may be seen as the ductus arteriosus closes. Ultimately, severe shock resulting in seizures, renal failure, liver failure, and worsening cardiac function may develop.

Whether these problems are reversible depends on both the severity and the duration of shock.

3 Causes

The causes of heart defects such as hypoplastic left heart syndrome among most babies are unknown.

Some babies have heart defects because of changes in their genes or chromosomes.

These types of heart defects also are thought to be caused by a combination of genes and other risk factors, such as things the mother comes in contact with in the environment or what the mother eats or drinks or the medicines the mother uses.

4 Making a Diagnosis

Making a diagnosis of hypoplastic left heart syndrome

Prenatal, or fetal, diagnosis

Made by fetal ultrasound. When you go for your routine fetal ultrasound, your doctor should be able to identify:

  • a four-chamber heart
  • two valves entering the heart
  • two valves and blood vessels exiting the heart

HLHS can be diagnosed on fetal ultrasound when the person performing the ultrasound notices that the left heart structures are small.

If HLHS is suspected, you should be referred to a fetal pediatric cardiologist for a fetal echocardiogram (a specialized fetal cardiac ultrasound).

Postnatal diagnosis

If HLHS wasn’t diagnosed prenatally, HLHS is usually diagnosed after the newborn baby shows signs of distress.

What is the value of diagnosing HLHS prenatally?

A diagnosis of HLHS through prenatal cardiac ultrasound enables doctors to plan to treat your newborn immediately after delivery. The family and medical team should plan for delivery at, or next to, a cardiac center that’s equipped to care for the newborn, such as:

  • a children’s hospital with an adult or obstetric hospital attached or very near
  • a medical center that has adult/obstetric care, as well as neonatal and pediatric cardiac services

Hypoplastic left heart syndrome may be diagnosed during pregnancy or soon after the baby is born.

During Pregnancy

During pregnancy, there are screening tests to check for birth defects and other conditions. Hypoplastic left heart syndrome may be diagnosed during pregnancy with an ultrasound, (which creates pictures of the body). Some findings from the ultrasound may make the health care provider suspect a baby may have hypoplastic left heart syndrome. If so, the health care provider can request a fetal echocardiogram, an ultrasound of the baby's heart, to confirm the diagnosis.

This test can show problems with the structure of the heart and how the heart is working with this defect.

After the Baby Is Born

Babies with hypoplastic left heart syndrome might not have trouble for the first few days of life while the patent ductus arteriosus and the patent foramen ovale (the normal openings in the heart) are open, but quickly develop signs after these openings are closed, including:

  • Problems breathing,
  • Pounding heart,
  • Weak pulse, or
  • Ashen or bluish skin color.

During a physical examination, a doctor can see these signs or might hear a heart murmur (an abnormal whooshing sound caused by blood not flowing properly). If a murmur is heard or other signs are present, the health care provider might request one or more tests to make a diagnosis, the most common being an echocardiogram.

Echocardiography also is useful for helping the health care provider follow the child’s health over time.

5 Treatment

Hypoplastic left heart syndrome is treated through several surgical procedures or a heart transplant.

Babies with hypoplastic left heart syndrome (HLHS) need surgery in the first weeks of life. They will have a series of surgeries to redirect blood flow through their heart.

Before surgery, your baby will need medicine (prostaglandin) that keeps the ductus arteriosus (the blood vessel between the pulmonary artery and aorta) open so blood can get to the rest of the body. Your baby may need help breathing or need to be on a breathing machine (ventilator).

HLHS is called a “single-ventricle heart defect” because there is only one pumping chamber in the heart. Single-ventricle defects are some of the most complex heart birth defects.


Surgery for HLHS does not give babies normal circulation. However, it may allow their heart to pump blood better to their lungs and the rest of their body.

The surgery is done in 3 stages during the first few years of life:

  • The first stage, called the Norwood procedure, is usually performed in the first weeks of life and is the most complex.
  • The second stage, called the Glenn operation, is usually performed between 4 and 7 months of age.
  • The last stage, the Fontan procedure, is usually performed around 3 to 4 years of age. The exact procedures and timing depend on your child’s condition, including how severe it is.

Stage 1: Norwood Procedure

The right ventricle is converted to the main pumping chamber and the aorta is made larger. A synthetic tube, called a Sano shunt, brings blood from the ventricle to the lung arteries. A large hole is created between the two atria to allow blood to pass easily between them.

Stage 2: Bidirectional Glenn Operation

The superior vena cava drains blood from the arms and head. In the Glenn operation, this vein is connected directly to the pulmonary arteries and the Sano shunt is removed.

Stage 3: Fontan Operation

In the final surgical stage, a synthetic tube is used to bring blood from the lower body directly into the lungs, bypassing the heart. After this surgery, the blood pumped to the body has full oxygen levels.
The goals of the surgeries are:

  • To create a new aorta that can carry enough blood out to the body and to connect this aorta to the right ventricle.
  • To separate oxygen-rich blood from oxygen-poor blood by:
      • Directing oxygen-poor blood, this comes from the organs and tissues of your child’s body, to blood vessels that go to their lungs, without going into their heart first. The blood picks up oxygen in the lungs.
      • Allowing oxygen-rich blood, this comes from your child’s lungs, to flow into their right ventricle. From there, it can be pumped to the rest of their body. 

Heart transplantation

This is an option in patients with failed medical and surgical procedures.

New Potential Treatments for Hypoplastic Left Heart Syndrome

Some babies may be too small or have other medical problems that increase the risk of the first-stage surgery (Norwood procedure) for HLHS.

A less complex procedure, called the hybrid procedure, combines surgery and cardiac catheterization. This may be a better option for these higher-risk newborns.

6 Lifestyle and Coping

Lifestyle modifications are necessary for your child in order to cope with hypoplastic left heart syndrome.


At the outset, appropriately warn the parents and other caregivers that hypoplastic left heart syndrome is a complex heart defect that requires:

  • multiple hospitalizations,
  • surgeries,
  • catheter interventions
  • and long-term follow-up.


Educate parents regarding the doses and side effects of their child's cardiac medications.

Discuss interactions with other medications with the family and the infant's general pediatrician.


Many infants require nasogastric or G-tube tube feeding after discharge from the hospital. Parents must become comfortable with placement of the nasogastric feeding tube and/or care for the G-tube, as the case may be.

Frequently, increased-calorie formula is required for adequate growth. Provide the formula recipe or a source for purchasing it to the caregiver.

Follow-up care

Stress the importance of follow-up care. If necessary, provide cab or bus vouchers to ensure compliance.

If noncompliance becomes a critical issue, physicians are required to report to the appropriate family services agency.

7 Risks and Complications

There are several risks and complications associated with hypoplastic left heart syndrome.

Without intervention, most infants with HLHS will not survive longer than a few days to a few weeks. Heart transplantation is an option, but because of the difficulty in obtaining a donor heart for an infant, the series of surgical procedures described above is most often recommended.

The first-stage procedure poses the highest risk for poor outcomes and death. Some specialized centers where a greater number of procedures are done have achieved survival rates that are higher than at centers where fewer procedures are done. Survival rates are higher with later stage procedures.

Infants and children who have the staged surgical procedures will require special care and treatment to support growth and nutrition. These children often have diminished physical strength as well as slowed developmental progress and may need support.

In the long-term, there is significant risk for progressive development of complications, such as:

  • heart failure,
  • heart rhythm problems,
  • protein-losing enteropathy,
  • and liver congestion resulting in cirrhosis.

Some cases will require heart transplantation to survive into adulthood.

Regular follow-up care at a center offering highly-specialized congenital cardiac care should continue throughout the individual's lifespan.

Consult your child's doctor regarding the specific outlook for your child.