The vectorcardiograpbic study on the right ventricular overloading was performed and obtained the following results. The materials used were 41 cases of congenital heart diseases and 21 cases of aquired heart diseases 1) There was no close relationship between the hemodynamic state and the spatial maximum QRS vector magnitude or the QRS half area axis in the horizontal plane or the QRS polar vector magnitude. 2) The shape of the QRS loop in the horizontal plane were classified into 2 groups, and each group was separated into 4 and 6 types. These types was found to be related closely with the right ventricular systolic pressure. This classification may be useful in assessing the severity and operative effect of the case with right ventricular overloading or diciding the operative indication. 3) The T loop has the tendency to be oriented toward left backward in the case of right ventricular diastolic overloading, and left forward in the case of right ventricuar systolic overloading.