Atrioventricular septal defect (AVSD) is a congenital heart condition that affects the septum, or wall, between the atria and ventricles of the heart. This defect is also known by a variety of other names, including atrioventricular canal defect, endocardial cushion defect, and complete atrioventricular canal defect. Some medical professionals may also refer to the condition simply as a heart septal defect. Regardless of the terminology used, AVSD is a serious condition that requires medical intervention to correct. Treatment may involve surgery or other procedures to repair the defect and improve overall heart function.