What Is a Single Ventricle Defect?

The normal heart has four chambers: two upper chambers called atria, which receive blood into the heart, and two lower chambers called ventricles, which pump blood out of the heart. Ordinarily, unoxygenated (blue) blood comes back from the body into the right atrium, moves into the right ventricle, and then is pumped out of the right ventricle through the pulmonary artery (the main artery to the lungs) to collect more oxygen. The now oxygenated (red) blood returns from the lungs and enters the left atrium, moves into the left ventricle, and then is pumped through the left ventricle's outflow tract to the aortic valve and out to the body through the aorta (the body’s main artery) – completing the cardiac cycle.

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A single ventricle defect, also called single defect anomaly or single ventricle physiology, refers to a variety of cardiac defects where only one of the heart’s two ventricles functions properly. The working ventricle may be either the left or the right ventricle. Sometimes, it is difficult to tell which pumping chamber is working properly. As a result of having only one functioning ventricle, all babies with a single ventricle defect have a "Y" shaped circulation where the blood flows from the heart to both the lungs and the body.

Forms of single ventricle defect include:

  • Tricuspid atresia (TA): the absence of the tricuspid valve that normally leads into the right ventricle. This leads to a hypoplastic (undersized) or absent right ventricle. Thus, blood cannot flow from the right atrium to the right ventricle. Pictured below:
  • Hypoplastic left heart syndrome (HLHS): the entire left side of the heart is so undeveloped that the left ventricle cannot pump blood to the body.
  • Mitral valve atresia (MVA): the mitral valve leading into the left ventricle is missing or closed off. This often occurs with hypoplastic left heart syndrome.
  • Double-inlet left ventricle (DILV): the right ventricle is not developed enough to function properly, and both atria feed into the only working ventricle (the left) via two valves.
  • Double-outlet right ventricle (DORV): both of the great arteries (the pulmonary artery and the aorta) are attached to the right ventricle, and no arteries connect to the left ventricle.
  • Cardiac heterotaxy defects (also called isomerism) where multiple different heart defects affect the heart, including abnormalities of the heart veins, valves, chambers, or outflow arteries. The word heterotaxy comes from hetero- (meaning different) and -taxy (meaning arrangement). This may lead to septal defects, or holes in the thin wall that divides the right and left sides of the heart. The heart’s valves and electrical system (which generates heartbeats) also may be affected. Sometimes, other organs also can be misplaced, including the intestines, stomach, liver and lungs. The spleen, which helps the body fight infections, may not work or may be missing.

What Are the Causes?

A single ventricle defect is a congenital (present at birth) condition and is among the most complex defects of the heart. This condition occurs in five of every 100,000 live births as the heart develops during the first eight weeks of the mother’s pregnancy. If you have a child with a congenital cardiac defect, the chance of having another child with a heart defect is about 2% to 3%, depending on the type of heart defect your child has. If your child’s defect affects the right side of the heart, the chance is slightly less than if it affects the left side of the heart.

How Is It Diagnosed?

Shortly after birth – usually within the first two months – a newborn with a single ventricle defect develops a bluish tint to lips, nails and skin (due to lack of oxygen), rapid or labored breathing, cold, clammy skin and a heart murmur – or whooshing sound – heard via stethoscope.

A single ventricle heart defect may be diagnosed during pregnancy with a fetal echocardiogram, which is a specialized ultrasound of the fetal heart. The affiliated physicians in the Fetal Cardiology Program at The Fetal Center will confirm a diagnosis and prepare a delivery plan for both mom and baby. A multidisciplinary team of specialists will also develop the baby's immediate care plan following delivery.

If a single ventricle heart defect is not diagnosed in utero, and suspicion of a heart defect occurs after the baby is born, a pediatrician will refer the patient to a pediatric cardiologist to determine the diagnosis.

The following tests may be utilized to find more details:

  • Pulse oximetry, a small and painless gadget placed on a finger, which may reveal low oxygen rates from an inefficient heart.
  • Chest X-rays, which create images of the heart and lungs, making major flaws visible, such as fluid buildup in the lungs.
  • A cardiac echocardiogram (ECHO), using sound waves (ultrasound) to produce images of the heart and blood vessels’ structures on a screen. This painless exam reveals whether the heart is pumping properly and whether too much or not enough blood is going to the lungs or the body as a whole. Occasionally, a single ventricle defect can be detected on a prenatal ultrasound, which will lead the doctor to order a more detailed prenatal cardiac echo.

In some cases, a physician also may order the following tests to confirm a diagnosis:

  • An electrocardiogram (EKG or ECG), a painless exam which checks the heart’s electrical action to reveal damage or irregular rhythms, suggesting problems with the heart.
  • A cardiac MRI (magnetic resonance imaging), a painless exam using radio waves, magnets and a computer to form three-dimensional images of the heart, which can reveal structural abnormalities (such as an enlarged ventricle).
  • Cardiac catheterization, which involves a thin, long tube that is inserted into a blood vessel at the belly button or groin and guided into the heart. The physician can see more details of a single ventricle defect and determine blood pressure and oxygen levels in the heart’s four chambers. At that time, the physician can also widen narrowed blood vessels to boost blood oxygen levels short-term.

How Is It Treated?

Short-term solution:

The short-term solution is to balance the amount of blood flow between the body and the lungs. If there is too much blood going to the lungs, blood flow must then be reduced by constricting the artery to the lungs (pulmonary artery banding). If the amount of blood going to the lungs is insufficient, an artificial blood vessel must be inserted to increase the blood flow to the lungs (Blalock-Taussig shunt).

In some cases, nothing needs to be done for the newborn with a single ventricle, as the blood flow between the body and lungs is already balanced. Surgery will be necessary, but can be deferred until the infant is older. In the most complicated situations, complex surgery is necessary to reconstruct the way blood flows to or from the heart. (This involves complicated open heart surgery, such as a Norwood procedure for hypoplastic left heart syndrome). For all newborns, however, there must be unobstructed blood flow to the body with a proper amount of blood flow going to the lungs. The issue of how to balance the blood flow between the body and lungs can be discussed with you by your doctor.

Long-term solution:

The long-term solution is an operation called the Fontan procedure. The Fontan procedure is where the blood that returns from the body is directly routed to the lungs without passing through the heart. Thus, there is no ventricle pumping blood through the lungs as there normally is. However, it does address important problems to help produce these results:

  1. The children are pink: All of the blood which goes to the body came from the lungs, so it is full of oxygen.
  2. No issues about balance between the lungs and the body: All of the blood that leaves the heart goes to the body, and then to the lungs and back to the heart. There is no "Y" shape in the circulation for an imbalance to occur.
  3. No extra work on the heart: The ventricle once again only pumps what the body needs; the ventricle's work has decreased from the newborn stage.

Although the Fontan procedure is the best that can be offered for single ventricle patients at this time, it is far from perfect. With a Fontan, there is no ventricle to pump blood through the lungs. Only the "pressure" within the veins drives blood through the lungs. If there is any significant resistance to flow through the lungs, a Fontan circulation may not be possible. Fontan procedures are usually performed at approximately 3-4 years of age.

Bidirectional Glenn Procedure:

Among doctors and nurses, a Fontan refers to the procedure where the two large veins draining unoxygenated blood back from the body (one draining the upper body and one draining the lower body) are connected directly to the lungs. In current medical practice, these are done at separate operations.

The upper vein is connected first (usually at about 6-8 months of age), and the lower vein is connected second (3-5 years of age).

The name "Fontan procedure" refers to the operation where the lower vein is connected, and the repair is complete. The first operation where the upper vein is connected is called a bidirectional Glenn procedure.

In a bidirectional Glenn procedure, the large vein that brings unoxygenated blood back from the upper body is connected directly to the lungs. This blood is oxygenated by the lungs and then returned to the heart. The blood that goes to the lower body goes directly back to the heart itself, and then gets repumped to the body without going to the lungs. Since unoxygenated blood from the lower body gets mixed in the heart with the oxygenated blood from the upper body and then is pumped to the body, the blood which goes to the body is not fully oxygenated. The usual oxygen saturation for a child with a bidirectional Glenn is around 75%-85%.

There are a number of reasons why the Fontan is staged, with the upper vein connected to the lungs at one operation and the lower vein connected at a different operation. The best explanation is that recovering from a Fontan can be very hard, and the heart has to be in the best shape possible in order for the Fontan to be successful. In the newborn stage, there is volume overload because the heart has to pump to both the heart and the lungs. Thus, hearts are generally dilated and not in perfect shape. A bidirectional Glenn does not require additional work by the heart and is not as hard to recover from as the complete Fontan; thus, a child whose heart is not in perfect shape will have a safer surgery with a bidirectional Glenn than with a Fontan. Also, it provides time for the lungs to adapt to the changes of not having blood pumped, but arrive passively via the Glenn circulation. When the Fontan surgery is performed, the heart is entering the operation in better shape after a bidirectional Glenn than if the Fontan was performed with the newborn circulation.

The risk and recovery of these operations varies from patient to patient, and will be discussed with you by your doctor.

What Are the Long-Term Effects?

There is good reason to have hope for babies born with a single ventricle defect. The national statistics for survival after the first surgery stage (the Norwood procedure) are very favorable. The hospital stay after a Norwood procedure can be up to six weeks or even more. A Norwood procedure is the highest risk surgery in the field of pediatric cardiovascular surgery – the surgery is performed on a newborn, the resulting blood flow pattern after surgery is not normal, and the surgery itself is very difficult. The chances of a child having a catastrophic event from the second and third operations are much less likely than the first procedure.

Although commonly accepted as the standard of care for single ventricle defect, the Fontan palliation sequence does not provide assurances that children will live a normal lifespan. With current medical technology, there is hope that most children will live into adulthood with few long-term complications. The reality for a child with a single ventricle defect is their heart will never be normal, but they may be able lead a relatively normal life. Ongoing research is being conducted to look at the neurodevelopmental and cognitive impact of single ventricle defect in order to improve current treatments and medical therapies.

What Follow-Up Care Is Needed?

Children with a single ventricle defect will need lifelong follow-up with a pediatric cardiologist. During the first few years of life, these visits will be almost monthly. After completion of the Fontan palliation, monitoring may be reduced to once or twice a year.

Prior to the second and third stage surgeries, a child will have to undergo a heart catheterization to evaluate the structures of the heart and measure pressure gradients within the heart and lungs. This catheterization will help determine the suitability of the next stage surgery. Unfortunately, some children are unable to undergo the second or third stage palliation. For some patients, despite positive results from surgery, the heart muscle becomes weak and consideration for heart transplant may become necessary.

Why Choose the Children’s Heart Institute?

At Children’s Heart Institute at Children’s Memorial Hermann Hospital, patients with congenital or acquired heart disorders receive hands-on specialized care 24/7 from a team of affiliated physicians and specialty-trained nurses who aim to deliver the best possible outcomes.

Children’s Memorial Hermann Hospital was named one of the top children's hospitals nationally in Cardiology & Heart Surgery by U.S. News & World Report. In addition, Children’s Heart Institute is among the top congenital heart surgery programs in North America for patient care and outcomes, according to the Fall 2019 Society of Thoracic Surgeons (STS) Congenital Heart Surgery Database Report of 118 STS participating programs.

In collaboration with various subspecialties, the affiliated team provides comprehensive care for newborns, children and adolescents, with the ability to transition into adult congenital cardiac care. Team members have the experience and skills necessary to offer innovative treatment methods and specialized services, including, but not limited to:

  • Biventricular repairs and biventricular conversions
  • Congenital heart optimization
  • Full repairs for complex congenital heart defects in newborns
  • Hybrid catheterization and surgical procedures
  • Minimally invasive transcatheter pulmonary valve (TPV) therapy
  • Minimally invasive repairs
  • Treatment for adult congenital heart disease
  • Valve repairs and preservation

With the Level IV Neonatal Intensive Care Unit (NICU) and a dedicated Children’s Heart Institute Intensive Care Unit at Children’s Memorial Hermann Hospital, critical heart patients have access to quality, specialized care. By utilizing state-of-the-art techniques, the team at Children’s Heart Institute strives to offer patients with the most complex problems the greatest opportunity for a normal life.

Contact Us

If you have any questions, use the online tool below to help us connect with you. To refer a patient or schedule an appointment, please contact our clinic using the information below.

  • Pediatric Cardiology Clinic
    The University of Texas Health Science Center Professional Building
    6410 Fannin, Suite 370
    Houston, TX 77030
    Phone: (713) 486-6755 (Appointment Line)
  • Pediatric and Congenital Heart Surgery Clinic
    The University of Texas Health Science Center Professional Building
    6410 Fannin, Suite 370
    Houston, TX 77030
    Phone: (713) 500-5746

To contact Children’s Heart Institute at Children’s Memorial Hermann Hospital, please fill out the form below.


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The Children’s Heart Institute is a collaboration between the affiliated physicians at McGovern Medical School at UTHealth Houston and Children’s Memorial Hermann Hospital. Typically, patients are seen on an outpatient basis at a UT Physicians clinic with all inpatient procedures performed at Children’s Memorial Hermann Hospital.

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