It is well known that the atrial myxoma is the most common intracardiac tumor which is hardly able to be diagnosed preoperatively and is completely curable if surgical treatment is appropriate. A case of the atrial myxoma, which was misdiagnosed as mitral valvular disease preoperatively and was successfully removed with the aid of the cardiopulmonary bypass, was reported. The common symptoms,signs,diagnostic measures and treatments of the intracardiac tumor were discussed with the review of literatures.[KTCS 1969;1:73-76]