Cardiac mensuration by the roentgenological heart volume method was carried out on 322 Korean school children,196 cases of male and 126 cases of female. Formula used in this study are as follows. Pradicted heart volume = K xBroad diameter x Long diameter x Greatest horizontal depth. Relative heart volume = Predicted heart volume (volumein ml) / Body surface area(Meter squared) The constant K represents the product of an ellipsoid area factor and acorrection factor for magnification of cardiac image. Therfore, K value used in this study is 0.42 for 200cm and150cm of focal film distances in posterior-anterior and lateral views respectively. Body surface area is obtainedby use of Du Bois Nomogram. The results were as follows; 1. Predicted heart volume at 6 years to 10 years of ageis 191.76+-4.66ml in male, 183.36+-3.64ml in female and at 11 years to 15 years of age 320.62+-10.34ml in male,284.22+-4.79ml in female. 2. Relative heart volume at 6 years to 10 years of age is 219.88+-6.19ml/m2 in male,211.43+-7.93 ml/m2 in female and at 11 years to 15 years of age 258.39+-6.85ml/m2 in male, 247.48+-9.14ml/m2 infemale. 3. In comparision with American standard value by Mannheimer, Korean school children show smaller heartvolume generally. 4. Roentgenological mensuration of the relative heart volume is considered to be simple and thebest method to express the standard of the heart size.