Hypoplastic Left Heart Syndrome

What is hypoplastic left heart syndrome?

Hypoplastic left heart syndrome (HLHS) is when the left side of the heart is not fully developed. It is a rare and serious birth defect.

A healthy heart works this way: 

  • Oxygen-poor (blue) blood comes from the organs and tissues of the body into the right atrium of the heart. Then it flows into the right ventricle, which pumps it to the lungs.
  • Oxygen-rich (red) blood comes from the lungs into the left atrium. Then the mitral valve opens, allowing blood to flow from the left atrium into the left ventricle. Next, the aortic valve opens, and the left ventricle pumps blood through the aorta and out to the organs and tissues of the body. 

In a child with HLHS: 

  • The mitral valve is small or missing.
  • The left ventricle is very small (hypoplastic) and cannot pump effectively.
  • The aortic valve is small or completely closed. 

Several other heart conditions are called hypoplastic left heart syndrome variants. They cause similar problems and have similar treatment plans.


Reprinted with permission ©2009, American Heart Association, Inc.

  • Because the left ventricle cannot pump enough blood to the body, the right ventricle must do all the work. Oxygen-rich blood from the lungs and oxygen-poor blood from the body come to the right side of the heart. The right ventricle then pumps this mixed-oxygen (purple) blood to both the body and the lungs.

    In a newborn, this can work for a short time because babies have an opening connecting their right and left atria (called the foramen ovale) and a blood vessel connecting their pulmonary artery to their aorta (called the ductus arteriosus). These connections normally close soon after birth.

    If these openings close in a baby with HLHS, little or no blood can flow through their heart to their body. This is why they need medical care as soon as they are born.

    The other risk for babies with this syndrome is that their right ventricle must do so much work. Over time, HLHS can cause heart failure.

    About 1 in every 4,000 babies has HLHS.

Hypoplastic Left Heart Syndrome at Seattle Children’s

USNWR BadgeOur heart team has treated many children with HLHS. We have years of experience with the medical and surgical treatment these patients require. Children with HLHS receive compassionate, comprehensive care through our Single Ventricle Program.

  • Our Heart Center is the top-ranked cardiology and cardiac surgery program in the Northwest and among the best in the nation, according to U.S. News & World Report. With more than 40 pediatric cardiologists, we have experience diagnosing and treating every kind of heart problem.

    Our outcomes for the surgeries needed to reconfigure the heart’s circulation system are among the best in the nation. We also have a pediatric cardiac anesthesia team and a Cardiac Intensive Care Unit ready to care for children who undergo heart surgery.

    We also have a Heart Transplant Program for children who need a transplant. Our team performs several transplants each year for children with HLHS or other heart problems that cannot be controlled using other treatments.

    Seattle Children’s has been treating children since 1907. Our team members are trained in their fields and in meeting the unique needs of children. For example, the doctors who give your child anesthesia (sedation) are board certified in pediatric anesthesiology. This means they have extra years of training in how to take care of kids. Our child life specialistsknow how to help children understand their illnesses and treatments in ways that make sense for their age.

  • Care often begins before a child is born, when their condition is diagnosed through our Prenatal Diagnosis and Treatment Program.

    We also have a special Adult Congenital Heart Disease Program to transition your child to adult care when they are ready. This program was developed by Seattle Children’s and the University of Washington to help with care throughout your child’s life.

  • When you come to Seattle Children’s, a team of people will take care of your child. Along with your child’s heart doctor (cardiologist), you are connected with newborn specialists (neonatologists), lung doctors (pulmonologists), nurses, child life specialists, social workers and others, if their expertise is needed. We work together to meet all of your child’s health needs and help your family through this experience.

    We’re committed to your child’s overall health and well-being. We’ll discuss treatments in ways you can understand and involve you in every decision.

    Read more about the supportive care we offer.

  • Before she was born, Poppy Dahl was diagnosed with HLHS. Watch her story of survival and learn how her care team worked to give her a fighting chance.

Symptoms of Hypoplastic Left Heart Syndrome

Most babies with HLHS develop symptoms within the first days after birth if not properly treated.

Common symptoms include: 

  • Bluish skin, lips or nailbeds (cyanosis) or pale skin
  • Being more tired than is normal
  • Trouble feeding
  • Fast breathing or working hard to breathe
  • Cold arms and legs
  • Weak pulse

Diagnosing Hypoplastic Left Heart Syndrome

  • HLHS can be diagnosed when a baby is in the womb using a fetal echocardiogram (fetal echo). This is a specialized ultrasound that uses sound waves to view and make pictures of a developing baby’s heart during pregnancy. The results are interpreted by a pediatric heart doctor (cardiologist) who specializes in fetal congenital heart disease.

    Your obstetrician may refer you for a fetal echo if your family has a history of congenital heart disease or if a routine prenatal ultrasound indicates a problem.

    We provide accurate diagnosis, thoughtful counseling and pregnancy management support through our Prenatal Diagnosis and Treatment Program.

  • To diagnose this condition, your doctor will examine your baby, check their heartbeat and pulse and listen to their heart.

    The doctor will ask for details about your child’s symptoms, their health history and your family health history.

    Your child will need tests that provide more information about how their heart looks and works. These may include:

Treating Hypoplastic Left Heart Syndrome

Babies with 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 1 pumping chamber in the heart. Single ventricle defects are some of the most complex heart birth defects.

We provide comprehensive care for children with HLHS through our Single Ventricle Program.

  • 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

    Stage 1: Norwood Procedure

    Reprinted with permission ©2009, American Heart Association, Inc.


    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

    Stage 2: Bidirectional Glenn Operation

    Reprinted with permission ©2009, American Heart Association, Inc.


    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

    Stage 3: Fontan Operation

    Reprinted with permission ©2009, American Heart Association, Inc.


    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, which 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, which comes from your child’s lungs, to flow into their right ventricle. From there, it can be pumped to the rest of their body.
  • The heart transplant team at Seattle Children’s performs numerous transplants each year for children with HLHS or other heart problems that cannot be treated with standard medical or surgical treatment. Read more about our Heart Transplant Program and our exceptional outcomes.

  • 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.

    Using a catheter, the heart doctor (cardiologist) widens the opening (foramen ovale) between the left and right atria and places a device called a stent in the ductus arteriosus to keep it open. Then the cardiac surgeon places bands on the pulmonary arteries to control the amount of blood flowing to the lungs. This approach allows the baby to grow and get stronger. During the second stage, the Norwood and Glenn surgeries can be done together with lower risk at 4 to 8 months of age.

Follow-Up Care for Hypoplastic Left Heart Syndrome

Outcomes for children with HLHS have improved dramatically in the past several decades. However, the period between the first and second surgeries is a particularly vulnerable time for these infants. Children will be cared for through our Single Ventricle Program, which focuses on the care and monitoring of infants with these severe heart problems.

Seattle Children’s is part of a nationwide group of children’s hospitals called the National Pediatric Cardiology Quality Improvement Collaborative (NPC-QIC) dedicated to improving the outcomes and quality of life for children with HLHS. The NPC-QIC provides additional family resources, support and information.

Adult Congenital Heart Disease Program

To meet your child’s long-term healthcare needs, we have a special Adult Congenital Heart Disease Program to transition your child to adult care when they are ready.

Contact Us 

Contact the Heart Center at 206-987-2515 to request an appointment, a second opinion or more information.

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