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Hypoplastic Left Heart Syndrome

What is hypoplastic left heart syndrome?

Hypoplastic left heart syndrome is among the most severe of all heart defects in children and is the most common heart defect from which children die in the first year of life.  Hypoplastic left heart syndrome represents 0.02% of all live births.

Hypoplastic left heart syndrome is an underdevelopment of the entire left side of the heart. Ordinarily, the right side of the heart pumps blood to the lungs, and the left side of the body pumps blood to the body. In children with hypoplastic left heart syndrome, the left side of the heart is underdeveloped to the point where it cannot effectively pump blood. Thus, the right side of the heart must do double duty and pump blood to both the lungs and the heart.

The blood vessels, which are meant to carry blood to the body (underdeveloped themselves), are still connected to the small left side of the heart. The blood vessels must be enlarged and connected to the right side of the heart and there must also be a way to get blood to the lungs. These corrections can be made during an operation called the Norwood procedure.

The Normal Heart

The normal heart has four chambers, two upper chambers called atria, and two lower chambers called ventricles. The job of each chamber is different, but, in general, the atria (top) receive blood into the heart, and the ventricles (bottom) pump blood out of the heart. Instead of thinking about the heart as having four chambers, it is often easier to think of the heart as having two sides. The right side of the heart pumps blood to the lungs, and the left side of the heart pumps blood to the body.

The cycle of blood through the heart and body begins when blood from the body is returned to the right side of the heart, and is pumped by the right ventricle through a large blood vessel called the pulmonary artery to the lungs. From the lungs, blood is returned to the left side of the heart, where it is pumped by the left ventricle out through another large vessel called the aorta to the body.

What will happen during pregnancy?

Hypoplastic left heart syndrome is a rare birth defect. Prenatal diagnosis is usually based on a fetal ultrasound that examines the heart and fetal anatomy. Once the condition is suspected, a targeted ultrasound is performed to rule out the presence of associated anomalies. A specialized ultrasound of the fetal heart, called an echocardiogram, will be performed, and an amniocentesis to look for chromosomal anomalies may be recommended. Although the ultrasound may be suggestive that there is an abnormality, the diagnosis will be confirmed after birth.

Your pregnancy will be closely monitored. The Center coordinator will keep you in contact with all of the appropriate physicians and specialists as well as coordinating the care for you and your baby after delivery.

Will a fetal treatment be required?

Currently, there are only experimental procedures for the fetal treatment of hypoplastic left heart syndrome with unknown long term results.  These are not offered at the Center.  If you and your fetus qualify for experimental interventions, the Center can help coordinate a referral to the appropriate facilities, if you desire.

What special considerations should be made for delivery?

Type of delivery - Typically, a cesarean delivery is not necessary unless there are other factors determined by your obstetrician.  A delivery plan will be carefully developed by your team of physicians at the Center and will be discussed with you and your obstetrician.

Place of delivery - The baby should be delivered at a hospital that is well prepared to handle babies with congenital heart defects.  There should be a neonatal intensive care unit with the capability to provide specialized care and pediatric cardiology and pediatric cardiovascular surgery services.

Time of delivery - There is usually no reason to intentionally induce early delivery.

What will happen at birth?

Immediately following delivery, doctors will carefully evaluate your baby. In most cases, there is no immediate danger to the infant. Your newborn will be transferred to the neonatal intensive care unit and stabilized. Your pediatric cardiologist will evaluate the baby. The newborn may need help with breathing and blood pressure.

Norwood Procedure to Treat Hypoplastic Left Heart Syndrome

The Norwood procedure is done within the first two weeks of life and represents an extensive operation. Approximately one-fifth of the babies who undergo the Norwood procedure will die during the first hospitalization and one-third will die within the first year.

The principle behind the Norwood procedure is that the only good pumping chamber (the right ventricle) must pump blood to the body. There is no natural, permanent connection between the right ventricle and the body. Thus, the Norwood procedure involves dividing the blood vessel that takes blood from the right ventricle to the lungs and rerouting it to take blood to the body. From that point forward, all of the blood which is pumped by the right ventricle heads toward the body.

By dividing the blood vessel to the lungs, the blood supply to the lungs is taken away. Part of the Norwood procedure involves restoring some blood flow to the lungs. There are two methods generally used:

  • Blalock-Taussig (BT) shunt - a small tube from the main blood vessel to the body (aorta or branch of the aorta) that connects to the pulmonary arteries 
  • Sano shunt - tube goes from the pumping chamber to the blood vessel to the lung

Both methods are accepted. The decision to use one versus the other is individualized.

Those who survive will need two more operations to completely fix the defect. The second operation is performed at roughly 6 months of age and the third procedure at approximately 3 years of age. Even those who survive through all three stages are still left with only one functioning pumping chamber. Thus, physicians think of the repair as "treating" the defect (palliation) rather than "fixing" it.

The Norwood procedure carries a high risk - multiple national studies show a risk of dying at 15-20% for the initial hospitalization, and close to 30% by one year of age. 


There is good reason to have hope for babies born with hypoplastic left heart syndrome. Although many die, many do live. Developmental studies on those that live show they have normal or near-normal IQ's and lead a good quality of life. The chances of dying from the second two operations are much less than the first, so those babies that make it through a Norwood procedure have a very good chance of doing well.

Contact Us

Pediatric Cardiology Clinic
University of Texas Health Science Center Professional Building
6410 Fannin, Suite 500
Houston, TX 77030

Phone: (832) 325-6516

Pediatric Cardiovascular Surgery Clinic
University of Texas Health Science Center Professional Building
6410 Fannin, Suite 950
Houston, TX 77030

Phone: (713) 500-7339

Note: This page is meant to be a helpful, informative introduction on the subject of hypoplastic left heart syndrome. The information may not be applicable to all cases, especially if there are additional defects. It is not meant to replace the opinion of a personal physician.