Cardiac volume mensuration by the roentgenological method was carried out in healthy 220 Korean adolescent, 116 males and 104 females. Predicted heart volume (PHV) and relative heart volume (RHV) were obtained from the following formulae : PHV = K $ imes$ Broad diameter $ imes$ Long diameter $ imes$ Greatest horizontal depth RHV = (total volume in ml)/body survace area (meter squared) The constant, K, represents the product of an ellipsoid area factor and a correction factor for magnification of the cardiac image. Therefore, K value used in this study is 0.42 for 200 cm and 150 cm of the focal-film distance in posterior-anterior and lateral views, respectively. The broad diameter was measured from the junction of the right atrium and the diaphragm to the junction of the pulmonary artery and left atrial appendage. The long diameter was taken from the junction of the superior vena cava and right atrium to the cardiac apex. The greatest horizontal depth of the heart was measured on laternal vie . Body surface area was obtained by use of the Du Bois nomogram. The results were as follows : 1. Predicted roentgenological heart volume at 16 years to 20 years of age was 449 $pm$ 11.1 ml in males and 418 $pm$ 7.7 ml in females. It increased with advancing age and height, but was not significantly infulenced by changes in body weight in both sexes. 2. Relative heart volume at 16 years to 20 years was 275 $pm$ 5.6 ml/$m^2$ in males, 327 $pm$ 4.1 ml/$m^2$ in females. It increased with advancing age and height, but was not significanlty influenced by changes in body weight in both sexes. 3. Roentgenological mensuration was a simple and reliable method in determining the cardiac volume.