Atrioventricular (A-V) canal defect (also called endocardial cushion defect or atrioventricular septal defect).

A large hole in the center of the heart exists where the wall between the upper chambers joins the wall between the lower chambers. Also, the tricuspid and mitral valves that normally separate the heart's upper and lower chambers aren't formed as individual valves. Instead, a single large valve forms that crosses the defect.

The large opening in the center of the heart lets oxygen-rich (red) blood from the heart's left side - blood that's just gone through the lungs - pass into the heart's right side. There, the oxygen-rich blood, along with venous (bluish) blood from the body, is sent back to the lungs. The heart must pump an extra amount of blood and may enlarge. Most babies with an atrioventricular canal don't grow normally and may become undernourished. Because of the large amount of blood flowing to the lungs, high blood pressure may occur there and damage the blood vessels.

In some babies the common valve between the upper and lower chambers doesn't close properly. This lets blood leak backward from the heart's lower chambers to the upper ones. This leak, called regurgitation or insufficiency, can occur on the right side, left side, or both sides of the heart. With a valve leak, the heart pumps an extra amount of blood, becomes overworked, and enlarges.

In babies with severe symptoms or high blood pressure in the lungs, surgery must usually be done in infancy. The surgeon closes the large hole with one or two patches and divides the single valve between the heart's upper and lower chambers to make two separate valves. Surgical repair of an atrioventricular canal usually restores the blood circulation to normal. However, the reconstructed valve may not work normally.

Rarely, the defect may be too complex to repair in infancy. In this case, the surgeon may do a procedure called pulmonary artery banding to reduce the blood flow and high pressure in the lungs. When a child is older, the band is removed and corrective surgery is done. More medical or surgical treatment is sometimes needed.

People with atrioventricular canal defect, before and after treatment, are at risk for getting an infection within the heart's walls or valves (endocarditis). To help prevent this, they'll need to take antibiotics before certain dental and surgical procedures.