Key Clinical MessageCor triatriatum is a rare congenital heart abnormality in which a membrane separates the left atrium (LA; sinister) or the right atrium (dexter) into two compartments. It is also a long‐forgotten cause of atrial fibrillation (AF) and substantially higher rates of blood stagnation, particularly proximal to the additional septum in the LA. In this case report, we faced a CHA2DS2‐VASc score of 1 in patients with non‐valvular AF due to Cor triatriatum sinister (CTS). The decision to start anticoagulants in this particular case was controversial, so we reviewed the literature to assess and address it. We present our case and discuss the indication of anticoagulants in this unique clinical scenario, accompanied by a literature review. Facing this dilemma of starting anticoagulants in special cases of CTS and AF should be individualized and need more investigation. However, till this moment, based on similar reports, it seems to be rational to consider CTS Per se as an additional risk stratification marker beyond the CHA2DS2‐VASc score start anticoagulant until the surgical resection. Considering CTS as the sole indication of anticoagulant in patients with normal sinus rhythm is a complex matter that needs further investigation.