By means of the lead X, Y, Z, the scalar recording of its component, a difference of the electrocardiogram was compared between the young and the old persons. They include the normal healthy and diseased ones. The former consisted of 88 elder and 32 younger persons. In this study, criteria of ventricular hypertrophy ere sought.P-wave showed a positive or diphasic one in the lead X, Y, but a negative in the lead Z. QRS-wave also showed a positive one in the lead X, Y, and a diphasic or positive, in the lead Z. T. wave showed a positive one in the lead X, Y, and a negative in the lead Z. The frontal QRS axis calculated from the lead X, Y, exhibited a correlation with the Eintoven's triangle, although the normal range of the former was narrower than that of the latter. It was found that the mean spatial T-magnitude was smaller in the younger aged groups than in the elder groups, in hypertensive patients an increase of the elevational QRS-V° was considered to be due a shift of the QRS vecthr to the left and posterior. It was also noted that the mean spatial QRS-T angle and QRS, T. magnitude were angmented. The mean spatial T-magnitude showed a decrease upon an elevation of the diastolic presure. Thus, it would seem that Rx+R=≧20mm is more quantitative method for criteria of the diagnosis of left ventricular hypertrophy. This leading method is found to be more quantitative method than ever before and to have fewer leading sited of the electrodes. Therefore, it may clinically be useful.