The technique of modifying an ECG to permit body surface recording of small-amplitude cardiac signals was a major step forward in the field of noninvasive clinical electrophysiology. Advances in the technique of high-resolution, or signal-averaged ECGs (SAECGs), have allowed the identification of clinical subsets of patients at high risk for ventricular arrhythmias, and provided for a better understanding of these arrhythmias. This text is written...