Heart and Blood Conditions

Hypoplastic Left Heart Syndrome

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    • For appointments in Seattle, Bellevue, Everett, Federal Way, Olympia, Tri-Cities and Wenatchee, call 206-987-2515.
    • For appointments in Tacoma and Silverdale, call 253-272-1812.
    • For appointments in Alaska, call 907-339-1945.
    • How to schedule

    If this is a medical emergency, call 911.

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  • Locations +

    • Seattle Children's Main Campus: 206-987-2515
    • Bellevue Clinic and Surgery Center: 425-454-4644
    • Everett: 425-304-6080
    • South Clinic in Federal Way: 253-838-5878
    • Olympia: 360-459-5009
    • South Sound Cardiology Clinics: 253-272-1812
    • Tri-Cities (Richland): 509-946-0976
    • Wenatchee: 509-662-9266
    • Pediatric Cardiology of Alaska: 907-339-1945
    • Seattle Children's doctors provide many cardiac services at regional sites throughout the Pacific Northwest. See our complete list of Heart Center locations.

  • Refer a patient +

    • If you are a provider, fax a New Appointment Request Form (NARF) (PDF) (DOC) to 206-985-3121 or 866-985-3121 (toll-free).
    • No pre-referral work-up is required for most conditions. If you have already done testing such as an EKG, Holter monitor or echocardiogram, please fax this information as well as relevant clinic notes and the NARF to 206-985-3121 or 866-985-3121 (toll-free).
    • Your patient will be seen as quickly as possible by the provider who is the best match for managing the current problem.
    • View our complete Heart Center Referral Information (PDF).

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.

Hypoplastic Left Heart Syndrome (HLHS)


Reprinted with permission www.heart.org. ©2009, American Heart Association, Inc.

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

Hypoplastic Left Heart Syndrome in Children

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

Our 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.

  • Care often begins before a child is born, when their condition is diagnosed through our Prenatal Diagnosis and Treatment Program.
  • Our outcomes for the surgeries needed to reconfigure the heart’s circulation system are among the best in the nation.
  • Through our Single Ventricle Interstage Clinic, we bring together experts in cardiology, nutrition, social work, feeding therapy and neurodevelopment to support your child’s health during the vulnerable transition between surgeries.
  • 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.
  • 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.
  • We have a special Adult Congenital Heart Disease Program to transition your child to adult care when they are ready. This program was developed by Children’s and the University of Washington to help with care throughout your child’s life.
  • U.S. News and World Report consistently ranks Seattle Children’s cardiology and heart surgery program as one of the best in the country.

Learn more about our Single Ventricle Program.

Saving Baby Poppy

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.


Contact Us

Contact the Heart Center at 206-987-2015 for a cardiac referral, a second opinion or more information.