Lipomatous hyperthrophy of the atrial septum is a rarely diagnosed but not rarely occurring benign hyperplasia of the lipomatous tissue. Apart from possible arrhythmias and single description of superior vena cava obstruction by extremely hypertrophied septum, lipomatous hyperthrophy does not seem to have any significant clinical importance. The potential danger is however associated with a false diagnosis of malignant tumor of the heart and unnecessary selection for cardiac surgery. We present two patients with the final diagnosis of benign lipomatous hyperthrophy of the atrial septum, referred to our center with an initial diagnosis of right atrial tumor.