Hypoplastic Left Heart Syndrome

Hypoplastic left heart syndrome is one of the two most complex congenital heart conditions. Babies with this syndrome become critically ill within the first few days or weeks of life. The heart defect is almost universally fatal if not treated.

In hypoplastic left heart syndrome, the left side of the heart (aortic valve, left ventricle, and mitral valve) is very small. In this syndrome, the left side of the heart cannot effectively pump blood to the body, so the right ventricle needs to take over.

Hypoplastic Left Heart SyndromeIn the normal heart, the right ventricle receives the blood returning from the body and pumps it into the pulmonary artery so that the lungs can oxygenate it. After returning from the lungs, oxygen-rich blood drains into the left heart; however, patients with a hypoplastic left heart syndrome have a dysfunctional left heart. Therefore, blood returning from the lungs must flow through an opening in the middle wall from the left atrium to the right atrium. This opening may be an atrial septal defect or patent foramen ovale. The right ventricle must pump this blood in addition to the blood coming in from the rest of the body. The right ventricle will be the only pumping chamber available for the blood to reach the lungs and the aorta (through a patent ductus arteriosus).

The newborn with hypoplastic left heart syndrome may look normal at birth, but within a few days may become critically ill as the ductus constricts and eventually closes spontaneously. It becomes extremely difficult for the right ventricle to pump blood forward into the aorta and the rest of the body as the ductus becomes extremely narrow and does not permit the blood to flow freely through the ductus. If the ductus constricts then the baby may go into a state of cardiogenic shock.

Symptoms may include:

  • Ashen in color (due to poor perfusion)
  • Rapid breathing
  • Lethargy
  • Nasal flaring
  • Cold and clammy skin
  • Shock
  • Breathing problems
  • Heart failure


Hypoplastic left heart syndrome is considered a congenital heart defect. This malformation occurs during pregnancy when the baby's heart is developing. The reasons for hypoplastic left heart syndrome are considered multifactorial. The cause remains unknown in many cases. A child born to a parent who has a congenital heart defect has a higher incidence of having hypoplastic left heart syndrome.

Over one-third of patients with hypoplastic left heart syndrome may have malformations in other parts of the body including the brain, kidneys and spleen.


Tests include an electrocardiogram, echocardiogram, chest x-ray, and blood tests. The echocardiogram is used to diagnose hypoplastic left heart syndrome. The study will show how underdeveloped (hypoplastic) is the left heart (mitral valve, aortic valve, left ventricle, and aorta). The Doppler echocardiogram will help assess the severity of the obstructions that may exist in the mitral and aortic valves as well as the aorta (coarctation of the aorta). The color Doppler echocardiogram will help analyze flow through the patent foramen ovale and patent ductus arteriosus. The echocardiogram will also help evaluate the heart's function (contractility).

The echocardiogram helps the surgeon determine which type of surgery is necessary.

The defect is not correctable, so some parents may choose to let nature takes its course. Babies can be treated with a series of operations or heart transplantation. Prior to surgery, the patent ductus arteriosus is kept open by means of medication called prostaglandin. An atrial septostomy may be necessary to help allow the blood from the left atrium pass more fluently into the right heart.

The operations are quite complex and need to be individualized for each baby. It is important for you to discuss all of the options available with your child?s doctor. If you agree to proceed with surgery, it will be done in several stages:

Norwood, stage 1
This surgery is usually performed during the first week of life. For the surgery to take place, the mid-bone of the chest needs to be open. There are several surgical procedures performed during the operation. The aorta is very narrow and needs to be reconstructed and united with the main pulmonary artery (which has been disconnected from its branches.) The surgeon will enlarge the patent foramen ovale or hole between the right and left atrium. This hole will permit oxygen-rich blood coming from the lungs into the left atrium to pass into the right heart, which will pump the blood into the newly created aorta. A modified Blalock-Taussig shunt (conduit) between an aortic branch (small artery) and one of the pulmonary artery branches is created in order to provide blood to the lungs so that it can get oxygenated.
Some surgical centers are doing a different type of surgery called the Sano procedure. In this operation the surgeon will connect a conduit (tube) between the right ventricle and the pulmonary artery. The surgery will allow the right ventricle to pump blood to both the lungs and the body.
Certain patients with hypoplastic left heart syndrome may undergo a hybrid procedure involving half surgery and half interventional cardiac catheterization. Long-term results of this type of surgery are yet to be determined. In rare cases, heart transplantation may be an option.
Norwood, stage 2
This surgery is also called a cavo-pulmonary anastomosis or bi-directional Glenn. This surgery is usually performed between three and eight months of age. The superior vena cava is detached from its distal part and connected to one of the pulmonary arteries. The Blalock-Taussig shunt is then removed. This surgery allows blood from the upper body to flow directly to the lungs to pick up oxygen and alleviate the workload of the heart.
Norwood, stage 3
This surgery is also called a modified Fontan procedure. Most patients undergo the Fontan procedure between one and four years of age. The surgery involves connection of the inferior vena cava directly to the pulmonary artery by means of a conduit or anastomosis (connection). The blood returning from the lower part of the body through the inferior vena cava will pass directly to the lungs, thus bypassing the heart and alleviating its workload. This connection results in establishment of a more normal oxygen level. The patients may require closure of a fenestration (hole) by means of interventional cardiac catheterization. There are several types of Fontan procedures that may be used depending on the situation or surgeon?s preference.

The goal of the Norwood operation is to allow the right ventricle to pump only oxygenated blood to the body and reduce mixing of oxygen-rich blood with oxygen-poor blood.

Rarely, babies may have other complex heart defects. For example, only one ventricle (single ventricle) may be present instead of two. Another possibility is that both the pulmonary artery and aorta may arise from the same ventricle (double outlet ventricle) instead of from separate ventricles.

These complex heart anomalies cannot be repaired with just one surgery. Instead, the heart defects must be operated on in several stages. If your baby has a complex cardiac abnormality, Dr. Villafañe can explain them by using a heart diagram, and discussing the surgical procedures available to your child. Communication between the cardiologist, primary care physician, surgeon, and the family are of utmost importance, particularly in these complex cases.

Remember that surgery is not curative. After the surgery, many patients have some degree of obstruction or leakage. Your child will require heart medications and continuing cardiology care. Serial echocardiograms are usually performed to monitor the heart size and function as well as to assess any leaky valve or obstruction.


Surgical mortality of Norwood stage 1 is anywhere between 5-40%. The mortality of Norwood stages 2 and 3 is much lower, less than 5%. Over 60% of patients with hypoplastic left heart syndrome survive the first year of life. Less than 5% will survive if left untreated. Over half of the patients are alive after five years of their Fontan procedure. Over three-fourths of those who survive the Fontan procedure are alive 15 years after their last surgery. About two-thirds are still alive 25 years after their Fontan.

Many patients who undergo the Fontan procedure will develop fast or slow heartbeats. The most common tachyarrhythmia is similar to atrial flutter. It is called interatrial reentry tachycardia (IART). Over 10% of patients experience atrial tachycardia by three years post-Fontan and almost 20% by five years. About half of patients may develop IART, atrial flutter, or atrial fibrillation 20 years post-Fontan. Most of these arrhythmias can be treated by means of ablation. Some patients may require surgery.

Virtually all patients will remain on aspirin or anticoagulants to help prevent clots, pulmonary embolism, and stroke.

The Fontan is considered a palliative surgery (not curative). Therefore, it helps many patients lead an almost normal quality of life if they refrain from strenuous exercise. In other words, most patients with the Fontan procedure will have some degree of exercise intolerance, which will not produce any significant symptoms while the patient is at rest or during mild exertion. These patients will have limitations to competitive sports or strenuous exercise. Complete evaluation is usually performed on a case-by-case basis prior to cardiovascular clearance for participation in certain types of low-intensity sports.

The risk of pregnancy is low (to moderate), depending on the heart's condition, the patient's symptoms, oxygen levels, residual abnormalities, and the presence of any arrhythmia. Almost 15% of pregnant ladies may experience some type of complications including arrhythmias, clot formation, stroke, and heart failure. The risk of a miscarriage is about 40%. Other risks to the fetus includes, low birth weight, stillbirth, and congenital heart defect that may involve left heart structures. Patients should consult with Dr. Villafañe prior to any pregnancy. Certain medications used for long-term treatment may affect the fetus.

Patients with this type of congenital heart defect may be at risk of endocarditis. The American Heart Association recommends optimal dental hygiene and semiannual dental appointments.

Patients who develop recurrent coarctation of the aorta may undergo an interventional cardiac catheterization with aortic angioplasty and/or aortic stent. A small percentage of patients with the Fontan procedure may develop severe heart failure and may end up requiring heart transplantation. About 10-20 percent of Fontan patients will end up requiring an artificial pacemaker.

The risk of sudden cardiac death is between 3% and 5%.

Long-term risks may include formation of clots, stroke, irregular heartbeats (arrhythmia), heart failure, gastrointestinal problems, laryngeal nerve paralysis, vocal cord problems, abnormal swallowing, formation of collateral vessels, pulmonary embolism, failure to grow, exercise intolerance, and others. In addition, about one-third of patients with this condition have attention deficit disorder, aggressive behavior, impulsivity, penmanship problems, lower mental IQ, and motor abnormalities.

Our Mission

Children's Heart Specialists, PSC is committed to provide comprehensive pediatric cardiac services to infants, children and young adults. We strive to insure the highest quality in non-invasive cardiovascular testing. Our medical staff is committed to being board certified in pediatric cardiology and adult congenital heart disease.

Our goal is to provide the highest quality of care with compassion and respect to our patients and their families.

Accredited in Echocardiography


We do not give any medical advice or recommendations about you or your child's health in this website. The medical information that appears on this website is to be used as a general guide about heart defects and symptoms. Medical advice is discussed at the time of your consultation with Dr. Villafañe.