A double interatrial septum (DIS) is a rare finding during echocardiographic evaluation and can often be mistaken for other more common atrial anomalies. The interatrial cavity created by the septum creates a low-flow state that increases risk of thrombus formation and thromboembolic events. Transesophageal echocardiography (TEE) plays a vital role in accurate diagnosis as a DIS is often not seen during transthoracic echocardiography (TTE). In this case, we report a patient who presented for surgery with a preoperative diagnosis of an atrial myxoma, was instead discovered to have a DIS, and then subsequently underwent DIS resection without complication. We discuss the differential of a DIS, including an atrial septal pouch, cor triatriatum, atrial myxoma, and aneurysmal interatrial septum and the classic features of each anomaly for appropriate diagnosis and management.