We studied a spatial and quantitative analysis of QRS and T waves by Frank-lead orthogonal electrocardiography (afterwards; ECG) in 50 cases of normal newborns, 30 cases of infants, 50 cases of adults, and also the variation in age was investigated. In the newborns, the comparative study was made serially, longitudinally in 21 infants with an early clamping of the cord and 29 infants with a late clamping of the cord. The results are mainly as follows. 1) The parameters reflecting the cardiac electromotive force of the right ventricle such as Sx, Qz and Sx+Qz decreased with aging. 2) Rx, i.e., the maximum leftward projection of QRS vector increased until the children, probably because the left ventricle was dominant in their growth and development and in the increased amount of work. A subsequent reduced value in the adults was considered to be mainly due to an increase of the distance between the heart and electrode by the increase in the thorax, particularly the transverse diameter and due to the growth in subcutaneous fat and muscle. 3) The values of Rx/Sx increased with aging. Rx and Sx in the adults were less than those in the children, but Rx/Sx was larger than that of Rx because Sx was less than Rx. 4) Age-related changes of Tz was most characteristic and was negative up to several days after birth. T vector was in forward direction and then turned positive (in backward). This was greatest at the period of the infants. Subsequently, it turned negative in the childhood, and extent was maximum in the adults.(ABSTRACT TRUNCATED AT 250 WORDS)