Primar99y cardiac tumors are rare and about 25% of primary cardiac tumors are malignant. A primary undifferentiated cardiac sarcoma, which very rare, is presented as follows: A 28-year old woman at the 32th week of pregnancy was admitted to the hospital because of dyspnea. A large intracardiac (left atrium) tumor was found with cardiac echocardiography and MRI. Emergency operation was performed under the diagnosis of left atrial myxoma. After Cesarean section, LA-tomy was done under the cardiopulmonary bypass. Tumor removal including endocardium of left atrium was done and final pathologic diagnosis was primary undifferentiated laft atrial sarcoma. After adjuvant radiotherapy, she has been followed up in out patient bases without problems up to now.