Cor triatriatum dexter of an adult

Cor triatriatum dexter is a rare congenital malformation in which a membran e divides the right atrium into two chambers. The membrane represents a per sistence of the right sinus venosus valve (RSV). Normally the RSV regresses between the 9th and 15th week of gestation, as the cephalic portion forms the crista terminalis and the caudal portion develops into the Eustachian a nd Thebesian valve. Any failure in the regression process may result in rem nants of RSV as a simple muscle bar, a Chiari-network or a fenestrated or u nfenestrated membrane (cor triatriatum dexter). We describe a patient with cor triatriatum dexter in whom diagnosis was made several years after succe ssful valvulotomy procedure for severe congenital valvular pulmonary stenos is.