In recent years the employment of roentgenologic methods has been advocated by numerous writers as a means of developing greater accuracy in the field of cardiac diagnosis. Notable among these have been Vaquez and Bordet1 and their co-workers in France, who have been largely responsible for the perfection of the orthodiascopic technic which has been so successful in their hands. Various measurements of the cardiac silhouette as obtained by teleroentgenographic or orthodiagraphic methods have been proposed, but in more recent times, following the work of Bardeen,2 these have usually been restricted to two, the area of the silhouette and its greatest transverse diameter. Cardiac area as determined by the planimeter measurement of the orthodiagraphic or teleoroentgenographic tracings is a measurement that can be made with surprising accuracy despite the fact that several writers have expressed doubt as to the ability of even the most experienced observer accurately to complete the