Atrioventricular septal defect (AVSD) is a congenital heart defect (present at birth). It is also known as cor biloculare. Additionally, there are several subdivisions depending on the size and location of the defect. Specifically, these subdivisions are atrial and septal and small ventricular septal defect, atrial septal defect primum, complete atrioventricular septal defect, incomplete atrioventricular septal defect, large atrial and ventricular defect, and transitional atrioventricular septal defect.