Bogotá, the capital of the Republic of Colombia, is situated at an altitude of 8,660 feet above sea level. This fact offered the opportunity to ascertain whether cardiac hypertrophy exists in normal persons living on the plateau. In roentgenologic studies carried out by Kerwin (1), in Oroya, Peru, 11,930 feet above sealevel, an increase of 11.5 per cent above normal standards was found in the heart size of the natives, and in x-ray studies carried out by Miranda and Rotta (2), at Morococha, Peru, situated at 13,840 feet, an increase of 21 per cent in the cardiac size of the inhabitants was established. Undoubtedly radiologic research has made possible more exact results in cardiac mensuration by the use of the orthodiagram or by teleroentgenography, since both procedures permit estimation of the real size of the heart image without any major error. I have, however, abstained from the use of the orthodiagram because this test involves subjective appreciation of the results without providing an impersonal graphic documentary record. Since in roentgenograms exposed at a distance of 6 to 6 1/2 feet the size of the cardiac shadow does not exceed the actual diameter by more than 5 per cent (3), it may be assumed that the teleroentgenogram gives us the real size of the heart of the person under examination. Though the variations of size observed between diastole and systole may produce variations in the transverse diameter by 1.5 to 2.0 cm., it has been found that in the majority of teleroentgenograms made at the moment of moderate inhalation no appreciable differences exist between the various test individuals because, as a rule, it happens that the heart film is obtained in the moment of diastole, which is the longest (3). I have refrained from estimating the heart area and the oblique and longitudinal diameters of the heart because, in order to obtain these measurements, it is necessary to determine by fluoroscopy the points at the right and left where the cardiac curve ends and the vascular curve begins, and this is subject to appreciable individual variations. It is for these reasons that a study was undertaken of the significance of transverse cardiac diameter, not, however, as an isolated measurement, but in relation to the weight and height of the persons examined. The little credit vouchsafed by clinicians and radiologists to radiographic measurements of the heart is due not to lack of mathematical precision but to the great individual variations found. These individual variations make it difficult to establish in a given case the exact limit of the normal. To give these measurements some value, it is necessary to relate them to the area to which the heart must supply blood in each particular instance, and this is accomplished by taking into consideration the weight and height of the subject.