A huge saccular idiopathic dilatation of the right atrium was detected with angiography and echocardiography in a 75 year old man. Cardiac catheterization data were compared with data obtained 4 years earlier. Idiopathic right atrial enlargement is not usually accompanied by tricuspid valve disease, but in this case tricuspid insufficiency did occur over a period of 4 years, possibly as a complication in the late stage of idiopathic right atrial enlargement.