An atrial septal aneurysm (ASA) is a rare but well-recognized abnormality of uncertain clinical relevance. It is a localized bulging of the inter-atrial septum into either or both atria during the cardiac cycle. ASA has been reported as an unexpected finding during autopsy but may also be diagnosed in living patients by echocardiographic techniques.We present a 37-year-old woman with a recurrent atypical chest pain of one-year duration. She was found to have a congenital atrial septal aneurysm on evaluation. The echocardiographic images mimicked a left sided cor triatriatum sinister. She had no other symptoms and had no co-morbidities. There was no audible murmur.ASA can mimic cor-triatriatum and echocardiographic examination should be performed from multiple views before any echocardiographic diagnosis is made.