Hypoplastic Left Heart Syndrome


Condition Description

Hypoplastic left heart syndrome (HLHS) is a severe congenital defect of the heart where the left side of the heart does not develop normally during early weeks of fetal development. The cause is unknown.

The left sided pumping chambers (left atrium, left ventricle) are very small and the two important valves (aortic and mitral) are either absent or underdeveloped. The flow of blood through the heart is very different because of the underdeveloped left side of the heart. Blood that comes from the lungs and contains oxygen flows through an opening between the upper pumping chambers (atrial septal defect, ASD) and then reaches the body through the ductus arteriosus that is connected to the aorta. Because the ductus arteriosus closes in the first few days of life the baby will seem normal initially and then become very ill once that vessel closes due to the reduced amount of oxygenated blood flow to the body. The baby's color will become grayish-blue because of the low level of oxygen (called cyanosis). The baby will have rapid breathing, difficulty feeding and will not survive beyond about six weeks of age without treatment. This condition accounts for 25% of the deaths from cardiac conditions in the first weeks of life.


Hypoplastic left heart occurs in about 2-4 per 10,000 live births. It affects 7-9% of all the children with congenital heart defects. It is somewhat more common in boys than girls (60-40% ratio).

Common Associated Conditions

Hypoplastic left heart syndrome occurs with increased frequency with certain chromosomal conditions such as Turner, Noonan, Smith-Lemli-Opitz, and Holt-Oram syndrome. Some other cardiac conditions that can occur with hypoplastic left heart include anomalous pulmonary venous connection, coarctation of the aorta, complete atrioventricular canal, coronary artery abnormalities, persistent left superior vena cava and endocardial fibroelastosis.

Short-term Treatment and Outcomes

Initially babies will be given medications such as digoxin to improve the heart function and diuretics to decrease the fluid load on the body. They will also receive an intravenous medication (prostaglandin) that will keep the ductus arteriosus open. They may also be given aspirin to decrease the blood's clotting. They will receive tests such as chest x-rays, echocardiograms, angiograms and heart catheterization to diagnose the heart problems. A chromosomal study will be done of children suspected to have a syndrome, and if a genetic condition is detected, the family will be offered genetic counseling.

Nutrition will be very important so that the baby will grow as well as possible and thus the heart will also increase in size prior to the surgeries. Hypoplastic left heart cannot be corrected but there are a number of options for treatment, including heart transplantation. Initially the drug that keeps the ductus arteriosus patent will lead to improved levels of oxygen in the blood going to the body. However, this is not enough to sustain growth and activity.

Decisions about what surgery is best for a baby with hypoplastic left heart are very complex, and each baby's situation is unique. If heart transplantation is not chosen, other procedures are done in stages. The first stage is called a Norwood procedure, and surgery is performed so that the right ventricle pumps blood to both the lungs and the body; the Norwood procedure must be done right after birth in order to be helpful to the baby. This will be followed at a later date (perhaps at six months of age) by other operations (such as a bi-directional Glenn procedure, a Fontan operation or a lateral tunnel surgery). These surgeries connect the veins bringing blood back from the body with the pulmonary artery to take blood to the lungs to receive oxygen. These second and third stage surgeries are complex and sometimes they have to be done a couple of times before the heart and body have good blood flow. These surgeries do not cure the condition but they can have fairly good results. About 80% of babies will survive a Norwood operation, and 95% a Fontan surgery. The overall survival at 5 years of age is about 70-75%.

An alternative to the multistage surgeries is heart transplantation, but this has the disadvantage in that the child has to then always take powerful anti-rejection drugs so that the body does not reject the new heart.

Long-term Treatment and Outcomes

Children who survive the first three stages of surgery do well. Very few require medications. Children will need to have frequent long-term follow-up with cardiologists, including stress tests to assess their limits for exertion. It will be very important to follow the children to be sure that their blood pressure remains normal and the heart valves are functioning well. Heart enlargement will also be assessed on chest x-rays as well as with echocardiograms.

Children with significant heart surgery histories have to take antibiotics when they have dental work because the bacteria in the mouth can be released into the blood stream and cause an infection in the heart (endocarditis).

Common Complications

Complications are many and varied. Scar tissue and leaky valves can lead to heart failure and continuing cyanosis as well as conduction problems (irregular or rapid heart rate). Pulmonary edema, pulmonary hypertension, and congestive heart failure are some of the complications that can occur and each must be treated promptly. Liver function will be checked if there is significant heart failure since there can be increased pressure into the portal system (blood vessels to and from the liver) that can damage the liver. Similarly, kidney function will be watched closely to be sure there is no kidney failure developing, especially if there is hypertension.

Implications for Children's Development

In the past, children with hypoplastic left heart conditions often had developmental delay due to the severity of their condition and episodes of low levels of oxygen in their blood. However, the fairly recent staged surgical procedures have changed the outlook for many children with this heart defect. Post-operatively their status may vary widely depending on the severity of the condition and effectiveness of the surgery.

If their surgery went well they will not need to have medications. They could have normal or near-normal development. If not in heart failure they are not restricted in their activity but they may self-restrict and need frequent rest periods. If they do have any degree of heart failure they should not compete in competitive activities where they might be pushing themselves beyond their level of endurance. Typically they will have normal intelligence if they did not experience episodes prior or during surgery where there was lack of oxygen to the brain.

For more information, including resources for parents and general information about congenital cardiac conditions, visit the following websites:

  • Lasting Imprint of MN: Lasting Imprint exists to create a supportive community that will inspire people to join in the fight against congenital heart defects through education, research, and assistance to heart families.