**1. Introduction**

Atrioventricular septal defects are a group of malformations involving the atrioventricular (AV) septum and common atrioventricular junction (**Figure 1**). Previously, referred to as atrioventricular canal or endocardial cushion defects, is now called AV septal defect (AVSD). For the purpose of this chapter, we will use the term AV septal defects. They are divided into complete, partial and variations of both of them based on the orifices and septal communications which will be discussed in detail in this chapter.
