Primary cardiac tumors are very rare. Atrial myxomas are the most common primary tumors and are commonly located in the left atrium. Myxomas can cause mitral valve inflow obstruction and can present with clinical signs and symptoms of mitral stenosis and the possibility of myxoma should be considered in differential diagnosis of mitral stenosis. Left atrial myxoma is rarely associated with rheumatic mitral stenosis. Transesophageal echocardiography plays a major role in the diagnosis of this tumor. We report a case of an extremely rare association between left atrial myxoma and rheumatic mitral stenosis. Because of its location and mobility, a thrombus in the left atrium may have a similar appearance to left atrial myxoma. However, a careful inspection of features of the left atrial mass may allow a diagnosis of left atrial myxoma. In our case, the site near the atrial septum, heterogeneous echogenicity, and detection of a stalk connecting the myxoma to the atrial septum were inspected. Such findings essentially exclude thrombus.