The natural history of this defect depends on the size of the communicating orifice between the upper and lower atrial chambers. If the communicating orifice is small, the patient is critically ill and may succumb at a young age (usually during infancy) to congestive heart failure and pulmonary edema. If the connection is larger, patients may present in childhood or young adulthood with a clinical picture similar to that of mitral stenosis.<unk>  may also be an incidental finding when it is nonobstructive. Diagnosis by ECHO, possibly followed by MRI.
Cor triatriatum
Phidippides cardiomyopathy
Algor mortis
Crisscross heart
Libman–Sacks endocarditis
Eales disease
Flutter valve
Hypertrophic cardiomyopathy