The authors describe the case of a 52-year-old patient with several hospitalizations due to acute pulmonary edema, clarified only during the performance of cardiac surgery for the correction of presumable mitral valvular pathology. A leiomiossarcome of the left auricle was concerned, which involved the posterior ring of the mitral valve, the interauricular septum and the orifices of the pulmonary veins. Due to the impossibility of proceeding with the complete resection of the tumor, the tumoral mass was wasted away in order to liberate the involved structures, this followed by chemotherapy. Two years since, the patient shows a generally deteriorated state, submitted to various hospitalizations due to cardiac insufficiency, having been objectivated hepatic metastization and recurrence of the primary neoplasm.