In double-outlet atrium either the right or the left atrium empties into both ventricles while the other atrium remains disconnected from the ventricular cavities. Cases of double-outlet atrium with a single atrioventricular (AV) valve have been reported but no cases of double-outlet left atrium and only two of double-outlet right atrium (one with three valves) have been reported. A description of the second case of double-outlet right atrium with two AV valves and a review of the other reported case are presented. Common anatomic characteristics were: two AV valves in the right atrium that connected with two normal ventricles; disconnection of the left atrium from the ventricular cavities; an atrial septal defect in a malpositioned atrial septum; and drainage of a left superior vena cava into the left atrium. Mitral incompetence was found in both cases. Clinical findings were similar to those seen in ostium primum atrial septal defect. Two-dimensional echocardiography and angiocardiography are able to accurately demonstrate this entity. Successful surgical correction was performed in both cases. Two morphogenetic hypotheses are proposed: abnormal development of the septum primum or primitive malposition of the common atrioventricular canal.