Atrioventricular canal defects (AVC) constitute 4–5% of congenital heart disease. AVC are a spectrum of malformations, characterized by a defect in the atrial septum, a defect in the ventricular septum and a defect in one or both atrioventricular (AV) valves. They are often referred to as “mixing lesions.” Depending on the size of the septal defects and the vascular resistances in the pulmonary and systemic circulations, deoxygenated blood from the right side of the heart and oxygenated blood from the left side of the heart will mix within the heart and determine the arterial oxygen saturation. AV septal defects are commonly associated with other major cardiac or extracardiac abnormalities. A thorough preoperative evaluation including a detailed physical examination, an echocardiogram, EKG, a chest X-ray, and possibly a catheterization is a must. Major postoperative complications include residual VSD or ASD, residual mitral regurgitation, complete heart block, and right ventricular dysfunction. The overall mortality for primary repair of a complete AV septal defect is <5%. Long-term survival is excellent and, in most cases, there is no need for further surgery.