Divided right atrium (prominence of the eustachian and thebesian valves).

Division of the morphologically left atrium (cor triatriatum) is a recognized clinical and surgical entity. Division of the right atrium (prominence of the eustachian and thebesian valves) is recognized pathologically, but is rare. It is unusual for this entity to be diagnosed during life. Stimulated by our experience with two patients seen at operation, one with an obstructive spinnaker-like formation and the other with a partitioned right atrium in the setting of pulmonary atresia, we reviewed the specimens in the heart museum of Children's Hospital of Pittsburgh that had prominence of the eustachian and thebesian valves. We identified 14 such hearts, which could be divided into two groups. In the first group, comprising six hearts, the valves were prominent in the form of Chiari networks and were of no functional significance. The valves were more extensive in the other eight hearts and partitioned the right atrium. In two of these, the valves themselves were the impediment to flow through the right side of the heart. In the other six, there was either atresia or severe stenosis along the right-sided pathways so that, after birth, the prominent valves retained their role during fetal life; namely, to deflect inferior caval venous return across the atrial septum to the left atrium. The partitions in these latter hearts would be of functional significance only if it were necessary to perform a Fontan procedure, when they might obstruct flow through an atriopulmonary (or atrioventricular) anastomosis.