We report a 73-year-old woman with primary cardiac leiomyosarcoma in the left atrium and ventricle. The tumor progressed very rapidly for 2 months after initial clinical evaluation. Obstruction of the left ventricular outflow tract and mitral stenosis were induced by the tumor. Urgent surgical resection was performed because she had cardiogenic shock due to paroxysmal atrial fibrillation. We could not resect the tumor completely because of severe invasion. She refused postoperative chemotherapy and radiotherapy, and died suddenly at home 89 days after surgery. To our knowledge, this is the first observation of mitral stenosis concomitant with obstruction of the left ventricular outflow tract in a patient with primary cardiac leiomyosarcoma.