Atrioventricular canal defect (endocardial cushion defect or atrioventricular septal defect) is a combination of several abnormalities in the heart present at birth (congenital abnormalities). It occurs when there's a hole between the chambers of the heart and causes problems with the valves that regulate blood flow in the heart.

Atrioventricular canal defect allows extra blood to circulate to the lungs which causes overwork and enlargement of the heart.

Often associated with Down syndrome, atrioventricular canal defect, if left untreated, may cause heart failure and high blood pressure in the lungs. In order to take care of this defect, doctors often recommend surgery during the first year of life to close the hole and reconstruct the valves.


Two common types of atrioventricular canal defect are:  partial atrioventricular canal defect and complete atrioventricular canal defect. The partial form involves only the two upper chambers of the heart. The complete form allows blood to travel freely among all four chambers of the heart. In both cases, extra blood circulates in the lungs.

The symptoms of complete atrioventricular canal defect usually appear in the first several weeks of life. They include: difficulty breathing (dyspnea), lack of appetite, poor weight gain and bluish discoloration of the lips and skin (cyanosis).  

The symptoms of a partial atrioventricular canal defect may not appear until early adulthood. When they do, the symptoms may be related to complications that develop as a result of the defect, and may include: abnormal heartbeat (arrhythmia), heart valve problems, heart failure and high blood pressure in the lungs (pulmonary hypertension).  


Atrioventricular canal defect occurs during fetal growth when the baby's heart is developing. Some factors, such as Down syndrome, may increase the risk of atrioventricular canal defect, yet in most cases the cause is unknown.

Risk Factors

Several factors may increase the risk of a congenital heart defect, including:

  • Down syndrome, a genetic condition resulting from an extra 21st chromosome.
  • Rubella measles or another viral illness during early pregnancy.
  • Inheriting a congenital heart defect from a parent.
  • Consuming alcohol during pregnancy.
  • Diabetes during pregnancy.
  • Some types of medications during pregnancy.


Potential complications include:

  • Enlargement of the heart.
  • Heart failure.
  • High blood pressure in the lungs (pulmonary hypertension).
  • Pneumonia.

Treatment greatly improves the outlook for children with atrioventricular canal defect, but later in life even some patients who have had corrective surgery may still be at risk of the following associated conditions:

  • Leaky heart valves (regurgitation)
  • Narrowing of the heart valves (stenosis)
  • Heart rhythm abnormalities (arrhythmias)
  • Breathing difficulties associated with damage to the lungs (pulmonary vascular disease)

The common symptoms of these complications include shortness of breath, fatigue and a rapid, fluttering heartbeat, among others. In some cases, such as a leaky heart valve, a second surgery may be needed.


In most cases, atrioventricular canal defect cannot be prevented. Consulting a genetic counselor and a cardiologist before getting pregnant is recommended.