Abstract. Even though rheumatismal valve diseases are recently reduced, they are still frequently seen in developing countries. Left atrial thromboses commonly may occur within the left atrial appendix in the presence of an atrial fibrillation and are adhered to the left atrium wall. The case we are presenting in this article demonstrated symptoms such as syncope and shortness of breath and controls carried out indicated an advance degree of mitral narrowing, determined by echocardiography and accompanied with a presence of a "free-floating" thrombus at the left atrial. Once pre-operative studies were performed, patient was operated. The "free floating" thrombus at the left atrial was removed, a mitral valve replacement was performed and the patient was discharged from our clinic without any complications, at post-operative 7th day. Key words: Mitral stenosis, thrombus, atrial fibrillation