Atrioventricular septal defects account for 4% of congenital cardiac malformations and over 50% of cardiac defects seen in Down syndrome. Clinical presentation is marked by congestive heart failure early in infancy. Cyanosis is rarely found in infants and suggests irreversible pulmonary hypertension or associated cardiac defects as tetralogy of Fallot, double outlet right ventricle, Ebstein anomaly, persistent left superior vena cava draining in the left atrium (Barbero Marcial, personal communication). Children with Down's syndrome is particularly difficult to assess because they often suffer from upper airways obstruction, which may contribute to the increased pulmonary vascular resistance determined at cardiac catheterization. This association of factors becomes a challenge for operability and, we will report one such case.