The signal-averaged electrocardiogram (ECG) is a simple, noninvasive test used to predict which patients may be prone to sudden cardiac death because of ventricular tachycardia. Signal averaging allows detection of low-amplitude waveforms in the ECG that are normally masked by noise. The averaging process is done by a computerized ECG machine. The results of abnormal signal-averaged ECGs can be used to predict ventricular tachycardia in patients after a myocardial infarction, with syncope, and after subendocardial resections. Application of the signal-averaged ECG in many other types of patients is currently being studied. The use of this diagnostic tool is rapidly increasing. Cardiac nurses should be aware of the methods and current research results of signal averaging.