The Todd and Karen Wanek Family Program for Hypoplastic Left Heart Syndrome (HLHS) is a research program with the goal of delaying or preventing heart failure for individuals with HLHS.

To learn more or to participate, please visit our website or contact

Follow the program on Facebook at Mayo Clinic HLHS, on Twitter @MayoClinicHLHS, and on Instagram at MayoClinicHLHS.

Recently Diagnosed

Hypoplastic Left Heart Syndrome

Your unborn baby has been diagnosed with Hypoplastic Left Heart Syndrome. What does this mean for your baby and your family?

Q. What is Hypoplastic left heart syndrome (HLHS)?

A. HLHS is a rare heart defect, affecting 1,000 newborns each year in the United States, in which the left side of the heart is severely underdeveloped, and the right side of the heart must pump blood to both the lungs and the body. The defect occurs during fetal growth and currently cannot be prevented.

In a healthy heart, the right side of the heart accepts blood from the rest of the body and pumps it to the lungs while the left side of the heart accepts blood from the lungs and pumps it to the body.When the left side of the heart is underdeveloped, the right side must perform both functions, pumping blood to the lungs and to the body.

During the first few days after a baby is born, the right side of the heart is able to do the job of both the right and left sides because of two processes. The first is through an opening, known as the foramen ovale, by which the blood flowing through the lungs can return to the right heart. The second process is by a blood vessel connecting the pulmonary artery to the aorta, known as ductus arteriosus, that allows the right side of heart to pump blood to the body in addition to the lungs. The majority of the time, the foramen ovale and ductus arteriosus close after a few days, leaving the heart with no way to pump the blood to the rest of the body.


Q. What causes HLHS?

A. At this time, the cause of HLHS is unknown and there is nothing to prevent it. The birth defect occurs in utero while the baby is developing. There is a very slight increased risk (less than ten percent) that families who have one child born with HLHS will have another child born with a heart defect.

Q. How is HLHS diagnosed?

A. Doctors will use an echocardiogram, also known as an ultrasound, to diagnose the heart defect. HLHS is often diagnosed in utero using a fetal echocardiogram.

Q. Will my baby need surgery?

A. Doctors will determine the exact treatment for your baby depending on the severity of the heart condition and the family’s wishes. The only treatment for HLHS is aggressive, early surgical intervention. The most common approach involves a three-stage surgical procedure. The operations are performed within the first few years of life and create reliable blood flow in and out of the functional heart chambers.

Stage 1: Norwood Procedure

The Norwood procedure is performed within the first few days of life to allow the heart’s lower right chamber, known as the right ventricle, to pump blood to the lungs and the body.


Stage 2: Glenn Procedure

The Glenn (or hemi-Fontan) procedure usually takes place between four and six months of a child’s life. The surgery reduces the amount of work the right side of the heart does by allowing it to pump blood mainly to the body and routing part of the blood returning from the body directly into the lungs.


Stage 3: Fontan Procedure

The Fontan procedure is performed on patients between 18 and 48 months old to connect the remaining blood vessels carrying blood from the body to the lungs. The purpose of this surgery is to allow the blood coming from the body to go directly to the lungs, normalize the oxygen levels, and reduce the right ventricle workload to the approximate levels of a normal heart.


Q. What happens after surgery?

A. After surgery, HLHS children need long-term surveillance of the reconstructed heart and often require heart medications. Regular appointments with a cardiologist will include echocardiograms, MRIs, blood tests, and heart catheterizations to ensure close monitoring of your child’s growing heart.

Q. What are the long term impacts of HLHS?

A. While science has made remarkable steps in treating patients with HLHS there is still no cure. Most patients will survive with treatments but may face other complications later in life. Some of these complications include heart arrhythmias, blood clots, developmental problems, and the possibility of future surgeries or a heart transplant. For more on this subject, please visit here.

Q. Are there new scientific advances that will help my baby in the future?

A. At the Mayo Clinic, we are making advancements to find new ways to treat HLHS through the use of four connected objectives: cell-based treatments, imaging and outcome, human genetics, and the creation of a biorepository. These advancements may delay and even prevent heart transplants for people with HLHS.

Cell-Based Treatments

Researchers believe stem cells can increase the strength of the heart, enabling it to pump blood through the body with greater power. By using cell-based therapies, team members are working to make the heart muscle stronger. This approach could possibly restore the right ventricle’s functional ability once it begins to decline or prevent the decline altogether.

The Todd and Karen Wanek Family Program for HLHS currently offers clinical trials to individuals with HLHS. The goal of the trials is to determine how stem cells derived from different sources in the body, delivered at different times, can strengthen the heart of individuals with HLHS. In one clinical trial, umbilical cord stem cells are collected after birth and delivered directly into the heart muscle during the Glenn procedure. Another clinical trial uses stem cells collected from an individual's own bone marrow to be injected into the heart.

Another use of stem cells includes comparing reprogrammed stem cells from children with HLHS and their unaffected parents to determine molecular differences in order to understand how HLHS develops.

Imaging and Outcomes

To better understand HLHS and the predictors of long-term right ventricular performance, researchers are comparing medical histories of HLHS patients by using ultrasounds and MRI images of their hearts. In addition, researchers are also improving the ability to assess right ventricular function noninvasively to detect declines in cardiac function as soon as possible so they can intervene in a timely manner.

Human Genetics

HLHS is likely caused by abnormal genes that result in the underdevelopment of the heart’s left ventricle. While those genes are currently unknown, researchers are analyzing whole-genome sequencing and bioinformatics to search for HLHS genetic variations. They are also attempting to detect changes in chromosomal material in people with HLHS.


By working with families to collect family histories, tissue and cell samples, genomic information and heart images of HLHS patients and their relatives, researchers are studying HLHS and creating a biorepository. The biorepository includes clinical and genetic data, as well as tissue and other physical specimens used to further study HLHS and to explore new treatment options.