Cardiac pseudoaneurysm, a sealed rupture of the heart, is potentially fatal if not repaired surgically. The incidence in children is low, and it has been described in connection with surgery involving the right ventricular outflow tract. We describe a case diagnosed 20 months after complete repair of Tetralogy of Fallot with a single coronary artery. The diagnosis was made with two-dimensional echocardiography and confirmed with right ventriculography. The pseudoaneurysm was corrected by emergency surgery without complications. We emphasize the importance of a high index of suspicion of this entity in these patients, who are often asymptomatic.