Based on the reconstruction of two-dimension phase space of time series of short ECG signals, the variation of the strange attractor geometry is described and two indices, VMI and VAI, are derived in this paper. The two indices can distinguish clearly the ECG signals of sinus rhythm, tachycardia and ventricular fibrillation. Stable results of VMI and VAI can be obtained by analyzing ECG signals of several seconds. They are expected to be used in the development of medical instruments for a fast realtime display of analysis results.