Abstract
A 37-year-old woman was admitted to Dong-A University Hospital for rapidly progressive congestive heart failure. Transthoracic echocardiography demonstrated a large mass with a stalk that appeared to be a myxoma on the posterior wall of the left atrium. However, the histological diagnosis was undifferentiated pleomorphic sarcoma. We report a case of primary undifferentiated pleomorphic sarcoma of the left atrium with acute pulmonary edema caused by mitral inflow obstruction.