Unusual case of new-onset heart failure due to cor triatriatum sinister.

We report the case of a 30-year old man who came to the emergency department of our hospital with acute left heart failure, and was diagnosed with a rare congenital anomaly (cor triatriatrum sinister), which can mimic a severe mitral stenosis. Cor triatriatum sinister is a rare anomaly (0.1% of all cases of congenital heart disease) that is seldom diagnosed in adult patients. The hallmark of this congenital defect is the presence of a fibromuscular membrane that divides the left atrium (LA) into two chambers: a postero-superior chamber into which the pulmonary veins drain and an infero-anterior chamber (true LA) containing the mitral valve and atrial appendage. Both chambers communicate through a membrane in which one or more drain holes can be found. When the hole is significantly obstructive, it results in increased venous and arterial pressures. Even though the definitive treatment of cor triatriatum is the surgical excision of the membrane, we present a balloon dilatation case with a good response to percutaneous therapy, both initially and in the ensuing months.