In 1952, CABRERA and MONROY stated that the electrocardiographic patterns of diastolic and systolic overload of the left ventricle were different and would make it possible to differentiate the former from the latter. In 1960, CABRERA and GAXIOLA reported the significant differences between the vectorcardiographic patterns of diastolic and systolic overload. On the other hand, SELZER et al., SEDZIWY et al. and YANO et al. were unable to find any significant differences between the two in either the electrocardiogram or the vectorcardiogram. The author made a statistical survey on the spatial and planar vectorcardiographic parameters of the diastolic and systolic overload of the left ventricle to try to differentiate the characteristics of the two groups. Material and Method : The following subjects were available for this study, including 56 patients with essential hypertension (above 160mmHg in systole and/or 90mmHg in diastole) as the samples of systolic overload of the left ventricle, 38 patients with patent ductus arteriosus (PDA) (below 35mmHg of right ventricular systolic pressure) as the samples of diastolic overload of the left ventricle, 39 patients with ventricular septal defect (VSD) (below 35mmHg of right ventricular systolic pressure) as the samples of both ventricular diastolic overload, and 116 normal adults as the samples of the controls. Frank lead system was used for vactorcardiographic recording. The frontal, horizontal and left sagittal planar vectorcardiographic loops were simultaneously photographed on 35 mm-film and the scaler electrocardiograms in the three orthogonal leads were also simultaneously recorded on the paper at the speed of 10 cm/sec. The following measurements of the vectorcardiographic loops and scalar ECGs were made : (1) direction and magnitude of the spatial maximum (max.) QRS and T vectors, spatial QRS-T angle, spatial T/QRS ratio, (2) direction of inscription of QRS loop in the three planes, (3) direction of the frontal max. QRS vector, direction and magnitude of the horizontal max. QRS vector, (4) amplitude of the initial max. rightward deflection (Qx). that of the max. leftward deflection (Qx) and ratio of the two (Qx/Rx), (5) amplitude of the max. anterior deflection (Rz), that of the mx. posterior deflection (Sz), and ratio of the two (Rz/Sz). (6) direction and magnitude of the spatial mean QRS (spatial QRS) and T (spatial T) vectors, spatial mean QRS-T angle. (7) spatial ventricular gradient (spatial VG).