Atrioventricular canal malformation, also known as endocardial cushion defect and atrioventricular septal defect, is a cardiac malformation caused by hypoplasia or arrest of the endocardial cushion during embryonic development. The lesions include upper atrioventricular valve, lower atrioventricular septal defect and abnormalities of the atrioventricular valve, forming a complex malformation ranging from a simple primary foramen ovale septal defect to a combination of both a giant septal defect and severe abnormalities of the second and third cusps. Atrioventricular canal malformations are rare, with an almost equal incidence in men and women. Because of the severity of the heart malformation, severe heart failure and pulmonary hypertension often develop in infancy. The clinical presentation of AV canal malformations varies according to the type of lesion, the size of the left-to-right shunt, the severity of AV regurgitation, and the elevated pulmonary vascular resistance. Most patients do not present with clinical symptoms in the early years of life, but grow up with pulmonary hypertension leading to obstructive pulmonary vascular disease, which can lead to palpitations and shortness of breath after exertion, reduced exercise tolerance, respiratory infections and right heart failure. Partial atrioventricular tract cases with poor physical growth and early onset of pulmonary hypertension may present with the aforementioned clinical symptoms and heart failure at an early age and continue to worsen. In cases of complete atrioventricular tracts, pulmonary hypertension and heart failure are present within 1 year or even 1 month after birth and worsen progressively. Rapid respiration, poor perfusion of the peripheral circulation, enlarged heart and cyanosis may occur, and death often occurs at an early age. About half of the patients have congenital dementia.