Hyuk An, M.D.Atrial myxoma constitutes the most significant of all cardiac neoplasm. About 75% occur in the left atrium and 25% in the right. They may cause severe and progressive disease mimicking valvular heart disease. But recently attention to differential point in the clinical features along with various diagnostic techniques have allowed pre-operative diagnosis in the most cases. From April, `77 to Aug., `78, three cases of left atrial myxoma and one case of right atrial myxoma were operated in Seoul National University Hospital. Pre-operative diagnosis was established with echocardiography and cardiac angiography. In all cases, tumors were resected with cardiopulmonary bypass successfully, and discharged with good results.[KTCS 1979;1:23-29]