Triatrial heart

Cor triatriatum is a rare congenital heart malformation resulting from abnormal development of the primary septum, which forms an anomalous membrane within the left atrium, dividing it into an accessory chamber and the true left atrium. Alternatively, it can be caused by incomplete fusion of the common pulmonary vein trunk with the left atrium, where the common pulmonary vein trunk forms the accessory chamber. It accounts for approximately 0.1% to 0.4% of congenital heart diseases, with a higher incidence in males than in females.