What is atrioventricular canal defect (AVC)?

Atrioventricular canal defect is really three heart defects in one disease that affects the middle structures (the crux) of the heart:

- An atrial septal defect (ASD), a hole in the wall of the heart that separates the two upper chambers (the atria). The hole allows blood to pass between the two chambers and leads to an abnormal and unhealthy concentration of blood on the right side. This is usually a primum (lower) ASD, though additional secundum (upper) ASDs may be present.
- An inlet ventricular septal defect (VSD), a hole in the wall between the heart’s two lower chambers (the ventricles). This stresses the heart and the blood vessels connecting it to the lungs because they must work harder to manage extra blood flow.
- A common atrioventricular valve. In a normal heart, two valves - the mitral and the tricuspid - help control blood flow between the upper and lower chambers of the heart. In atrioventricular canal defect, the two valves are combined into one, resulting in a common atrioventricular opening (or canal).  

Atrioventricular canal defect is much more common in children with Down syndrome than in other children. Forty percent of all children with Down syndrome have congenital heart disease and, of those, 40 percent have atrioventricular canal defect. Atrioventricular canals are also called AV canals or endocardial cushion defects.