cor triatriatum /kôr trī·ā′trē·ā′tum/ , a congenital anomaly caused by failure of resorption of the embryonic common pulmonary vein, resulting in division of the left atrium by a fibromuscular diaphragm, the posterosuperior chamber receiving the pulmonary venous return and the anteroinferior chamber communicating with the left atrial appendage and mitral orifice. This results in a heart with three atrial chambers. The orifice between the two compartments may be reduced or absent, producing pulmonary venous obstruction.
