Scintillation angiocardiography was performed around the point of time when the injected RI mainly passed through the left ventricle. Gating permitted the radiophotography of the end-diastolic and end-systolic image of the left ventricle. Critiques of the techniques gave result that the best available image could be obtained when the cumulative count was 20,000, aperture setting 4/5 and brightness of cathode ray tube 8. Studies with mechanical model showed that the condition of high-flow, combined with the use of relatively small dose of RI resulted in a marked underetimation of the left ventricular image. Clinical studies was performed using SWI-LVEDV plots, giving the plot of stroke index (SWI) against the left ventricular end-diastolic volume (LVEDV). It was thus formed that the patients with enlarged left ventricles responded to the administration of digitalis with shrinkage of the heart, while the patients with relatively small heart responded to it with increase in SWI at the unchanged level of LVEDV. Studies with systolic time intervals particularly PEP/LVET, showed that relatively high values of PEP/LVET applied to those whose left ventricular SWI-LVEDV plots were located low and to the right, while relatively low values of PEP/LVET applied to those patients whose SWI-LVEDV plots were located high and towards the left, indicating relatively good LV performance.