T-wave alternans is a change, in the microvolt range, of T-wave amplitude on an ABABAB sequence. At present, various groups of patients have been evaluated, including those with myocardial infarction, congestive heart failure, implantable cardioverter-defibrillators and a clinical indication for programmed ventricular stimulation. In all clinical conditions analyzed, T-wave alternans analysis demonstrated a good diagnostic accuracy, suggesting a possible clinical use of the test in these settings.