Divided left atrium with obstruction of pulmonary venous return in the setting of hypoplasia of the left heart.

We describe an infant with hypoplasia of the left heart diagnosed prenatally who, at birth, had signs of severe pulmonary venous obstruction. Echocardiography indicated normally connecting pulmonary veins, and showed a paradoxical right-to-left shunt across a patent oval foramen. Postmortem examination revealed that the obstruction was due to a divided left atrium, or cor triatriatum sinister, with an imperforate muscular diaphragm separating completely the two components of the divided atrium.