The left ventricular muscle volume (LVMV) was determined echocardiographically and the radius of the circle with equal circumference to the thorax (R1) was calculated from thorax-circumference in 688 children as a part of the Shimane Heart Study. correlation of the summed precordial voltage (SV1 + RV5) with LVMV was not close (r = 0.377 in boys and -0.095 in girls). The precordial voltage (SV1 + RV5) was corrected by the square of R1 to compensate for the diminution of electrical potential by distance. Correlation between (R1) 2 x (SV1 + RV5) and LVMV was good in boys (r = 0.681) and relatively good in girls (r= 0.554). This fact indicates that LVMV can be predicted from ECG and anthropometric measurements of thorax without using echocardiography. Therefore, (R1) 2 x (SV1 + RV5) seems to have clinical applicability as the index of LV size, if the differences in (R1) 2 x (SV1 + RV5) and in the correlation coefficient between both sexes are clarified further.