Cor triatriatum masked by primary pulmonary hypertension.

In a 17-month-old boy with clinical signs of right heart failure, the diagnosis of primary pulmonary hypertension was made, based on cardiac catheterization findings with high pulmonary arterial pressure and normal pulmonary wedge pressure although two-dimensional echocardiography demonstrated a left atrial membrane. Postmortem examination confirmed a left atrial membrane (cor triatriatum), and the microscopic examination revealed the histological pattern of primary pulmonary hypertension. Due to reduced pulmonary blood flow, pulmonary venous obstruction was masked and could not be assessed by measuring pulmonary wedge pressure.