Atrioventricular septal defect is an opening between all four chambers of the heart that is present at birth (congenital heart defect). The opening is caused by a failure of heart tissue to come together during the growth of the fetus.

Atrioventricular septal defect results in a large opening in the center of the heart, with a hole between the 2 lower chambers (ventricular septal defect) and between the 2 upper chambers (atrial septal defect).

Atrioventricular septal defect requires surgery to correct.