Right atrial and tricuspid hypoplasia.

Cor triatriatum dexter is a rare cardiac anomaly with division between the sinus and primitive atrial portions of the right atrium. It is supposed that the failure of the venous valves to regress appropriately may create abnormalities in fetal circulation predisposing the fetus to maldevelopment of the right heart structures. The underdevelopment of the right ventricle with hypoplasia or atresia of the tricuspid valve is a well known abnormality, but underdevelopment of the right atrium with tricuspid hypoplasia due to multiple venous valves is extremely rare. This is a case of complex type of cor triatriatum dexter in which the right atrium is hypoplastic and like a tube formed by the superior and inferior vena cava and is divided into 3 portions by 2 membranes.