Atrioventricular septal defects constitute a group diseases with incomplete formation of atrioventricular canal formed by the atrioventricular cushions, in other words incomplete morphological development of the part of atrial septum formed by septum primum, atrioventricular valves and ventricular septum in various degrees. Atrioventricular septal defects constitute up to 3% of all congenital cardiac diseases. It is closely associated with Trisomy 21 anomaly and one third of these individuals may have some form of atrioventricular septal defects. Major determinants of the clinical picture are the amount of left-to-right shunt, the degree of left atrioventricular valvular insufficiency and the type/severity of the co-existing cadiac defects. With advanced cardiocascular surgery techniques and growing experience in pediatric cardiac surgery, the perioperative mortality rate for the repair of this type of defects decreased up to approximately 1%. Satisfactory results have been reported during the long-term follow-up of the patients.