The purpose of this study is to measure cardiothoracic ratio and to report the opinions on it, targeting 500 persons who were conducted simple chest radiography, in terms of clinical symptom, by visiting a medical examination center for S university hospital. As to the general characteristic of 500 research targets, it comprised 263 persons (52%) for males and 237 persons (48%), and the average age is 49.4. Out of 500 persons, it showed 125 persons (25%) in their thirties, 125 persons (25%) in their forties, 125 persons (25%) in their fifties, and 125 persons (25%) in their sixties. 1. In terms of the wholly 500 targets, the average value of cardiothoracic ratio was 0.48, and the average cardiothoracic ratio showed 0.45 in their thirties, 0.46 in their forties, 0.50 in their fifties, and 0.53 in their sixties. 2. The minimum value of cardiothoracic ratio was 0.33, and its maximum value was 0.70, and it showed 319 persons (63.8%) as to a case lower than 0.5, which is a normal value, and 181 persons (36.2%) as to a case more than 0.5, which is a normal value. 3. Among 181 persons who showed cardiothoracic ratio higher than normality, it showed 17 persons (9.4%) in their thirties, 22 persons (12%) in their forties, 54 persons (30%) in their fifties, and 88 persons (49%) in their sixties. 4. The average for the internal diameter (ID) of thorax was 141.8 mm, 229.6 mm at the minimum, and 353.5 mm at the maximum. 5. The average for the maximum transverse diameter of right side of the heart (MRD) was 48.0 mm, 4.95 mm at the minimum, and 84.5 mm at the maximum. The average for the maximum transverse diameter of left side of the heart (MLD) was 93.5 mm, 56.7 mm at the minimum, and 138.5 mm at the maximum. 6. The average for TD (MRD+MLD) of the heart was 292.6 mm, 96.6 mm at the minimum, and 199.2 mm at the maximum. 7. The average of cardiothoracic ratio (MRD+MLD/ID) was 0.48, 0.33 at the minimum, and 0.70 at the maximum.