A preliminary investigation has been carried out concerning the values corresponding to the transverse diameter of the heart, the frontal area of the cardiac silhouette and the diameter of the aortic arch. These measurements have been determined in radiographs of the chest, taken at 2 meters (6 feet) distance, in 107 subjects living at sea level and in 250 residents of Morococha, at 4,540 meters of altitude. All the subjects were healthy males, of en age between 18 and 35 years. The prediction of the normal values corresponding to these measurements has been obtained from the tables and nomograms of Ungerleider and Clarck. The results obtained at sea level demonstrated that it was possible to utilize these comparative values: 94.5 % of the transverse diameter measurements tell within the normal variations given by Ungerlayder and Clarck; the frontal area measurements showed wider variati...