Both a pericardial effusion and a failing myocardium can produce the roentgen appearance of a large, smoothly dilated heart which shows little evidence of pulsations. The correct diagnosis is often suggested by the appearance of the hilar vessels which are usually obscured by the cardiac shadow that is enlarged by a pericardial effusion, and not by the failing heart with dilatation of its chambers. Displacement of the epicardial fat line within the cardiac silhouette can be pathognomonic for a pericardial effusion. A normal pericardial shadow outlined by epicardial and retrosternal fat lines, seen on the lateral chest film, will exclude a pericardial effusion from consideration. A conclusive diagnosis of a pericardial effusion can be made by angiocardiography.