A patient rapidly developing right heart failure due to a left-atrial leiomyosarcoma was admitted for surgery. A large tumor, originating in the left atrium and extending into both pulmonary veins, was removed. Histology showed an unusual epitheloid appearance of many cells with occasional mitoses and a strong immunexpression to desmin and actin. Six months later heart failure developed again: computer tomography demonstrated regrowth of the tumor in the left atrium with invasion of the mediastinum and the para-aortal lymph nodes. The patient died shortly after.