<unk>  dextrum is extremely rare and results from the complete persistence of the right sinus valve of the embryonic heart. The membrane divides the right atrium into a proximal (upper) and a distal (lower) chamber. The upper chamber receives the venous blood from both vena cavae and the lower chamber is in contact with the tricuspid valve and the right atrial appendage.
Cor triatriatum
Phidippides cardiomyopathy
Algor mortis
Crisscross heart
Libman–Sacks endocarditis
Eales disease
Flutter valve
Hypertrophic cardiomyopathy