A method and apparatus for analyzing characteristics of ECG signal data having a succession of waveforms produced by the beating of the heart. ECG signal data is obtained from a patient. A depolarization feature and a second feature of the waveforms of the ECG signal data are determined. Waveforms of the ECG signal data having a stable heart rate are selected for use in determining the second feature. Waveforms selected are those having minimum depolarization feature standard deviation and minimum depolarization feature dispersion. The depolarization feature and second feature for the heart beats of the selected waveforms are displayed.
