Complete atrioventricular septal defect is a congenital heart disease characterized by an ostium primum atrial septal defect, a common atrioventricular valve and a variable degree of posterior ventricular septum defect. Complete atrioventricular septal defect accounts for about 3% of congenital heart diseases and occurs in two out of every 10.000 live births. It is closely associated with Down syndrome and 40-45% of patients have Down syndrome. According to Rastelli's classification, three types of complete atrioventricular septal defect have been described (Rastelli type A, B, and C) based on the morphology of the superior bridging leaflet of the common atrioventricular valve. The atrial and ventricular defects in complete atrioventricular septal defect lead to a high pressure and volume load in right ventricle, resulting in the development of pulmonary hypertension and congestive heart failure in these patients. Congestive heart failure symptoms appear in early infancy The diagnosis and the evaluation of anatomical details are performed by echocardiographic examination. Over time, pulmonary hypertension becomes irreversible, thus precluding the surgical therapy. Medical treatment plays only a minor role and the goal of the medical treatment is to maintain the condition of the patients in a good level until surgery. The surgery should be performed before the development of pulmonary vascular disease and the first 3-6 months is generally preferred.