Frank's lead system vectorcardiogram (VCG) was used to record the ventricular arrhythmias (VA) of different areas induced by pacing in 22 canines and by stimulating the epicardium of different areas in 8 patients of mitral stenosis during operation. The results showed that VCG can localize the origin of VA of 13 areas in canines and 9 areas in human. To localize the VA at or near ventricular septum VCG is more accurate than ECG (94% vs 70%).