Atrioventricular Canal Defect

What is atrioventricular canal defect?

An atrioventricular canal defect, or AV canal, is a combination of several closely associated heart problems that result in a large defect in the center of the heart. Also known as atrioventricular septal defect or endocardial cushion defect, the condition is congenital, which means it is present at birth, and occurs in two out of every 10,000 newborns. It is often associated with Down syndrome.

When the heart is properly divided, blood from the lungs does not mix with blood from the body; however, with an AV canal, blood moves freely among the four heart chambers. If left untreated, AV canal can cause many problems involving the heart and lungs.


Like many congenital heart conditions, AV canal defect isn’t actually a single defect but rather a group of closely associated defects in various combinations and with varying degrees of severity:

  • atrial septal defect
  • ventricular septal defect
  • abnormalities of the AV valves (mitral and tricuspid) that separate the upper heart chambers (atria) from the lower chambers (ventricles), often resulting in one large “common” valve rather than two separate valves

In addition, there are other associated heart defects such as patent ductus arteriosus, transposition of the great arteries, unbalanced AV canal defects, and aortic arch hypoplasia.

What are the symptoms of atrioventricular canal defect?

A child with atrioventricular canal defect (AV canal) will usually develop symptoms within the first few weeks to months of life. These symptoms may include:

  • disinterest in feeding, or tiring while feeding
  • poor weight gain
  • fatigue
  • sweating
  • pale skin
  • cool skin
  • rapid breathing
  • heavy breathing
  • rapid heart rate
  • congested breathing
  • blue color

If your child has any of these symptoms, your pediatrician will probably refer you to a pediatric cardiologist for testing, diagnosis, and a determination of treatment.

What causes atrioventricular canal defect?

When the heart is forming during the first eight weeks of fetal development, it begins as a hollow tube. Over time, partitions that form within the tube eventually become the walls dividing the right side of the heart from the left.

Atrial and ventricular septal defects occur when the partitioning process doesn’t occur completely, leaving openings in the atrial and ventricular walls. The valves that separate the upper and lower heart chambers are formed toward the end of this eight-week period, and often they don’t develop properly. Frequently, instead of two separate AV valves (tricuspid and mitral valve), there is a single large common valve that sits between the upper and lower chambers of the heart, allowing blood to flow freely between the chambers above and below the valve — mixing oxygen-rich and oxygen-poor blood.

Do genetics play a role in atrioventricular canal defect?

Genetics may play a role in the development of AV canal defect. Many children have associated genetic syndromes. About 15 to 20 percent of children with Down syndrome also have AV canal defect.

How we care for atrioventricular canal defect

At Boston Children’s Hospital our Cardiac Surgery team treats some of the most complex pediatric heart conditions in the world, with overall success rates exceeding 98 percent — among the highest in the nation among large pediatric cardiac centers. In particular, the methods used to repair an AV canal defect have improved greatly in the past two decades, and the operation has a high likelihood of success.

Our areas of innovation for atrioventricular canal defect

The Boston Children’s Hospital Benderson Family Heart Center deals with the most complex AV canals, which often include children operated on at other centers. We are committed to constantly refining and improving our techniques and procedures.

Children with unbalanced AV canal, traditionally treated as single ventricle defect, are now being considered for biventricular repair. This is achieved using innovative techniques, developed in Boston Children’s Complex Biventricular Repair Program, and refined with 3-D printed hearts in the lab, to ensure the repair is durable throughout a lifetime.