Ecchinococcal infestation of the heart accounts for only 0.5-2% of ecchinococcosis cases. A case is reported of right atrial hydatid cyst associated with rheumatic mitral valve disease in a 43-year-old woman. Physical examination and chest X-radiography revealed mitral disease. Transthoracic and transesophageal echocardiography demonstrated a single, large cystic mass of 4 x 4 cm located in the right atrium, and heavily calcified mitral rheumatic disease with commissural fusion. Confirmatory computed tomography and magnetic resonance imaging excluded other extracardiac locations. Radioisotopic lung perfusion scanning and angiographic scanning excluded pulmonary embolism. The patient underwent mitral valve replacement and the hydatid cyst was excised. An intraoperative examination and subsequent pathology confirmed a diagnosis of hydatid cyst.