The aims of the present study were to compare the amplitude of J waves by measuring slope and duration in patients with Early Repolarization (ER) syndrome and healthy athletes with ECG evidence of J-point elevation associated with J wave and to evaluate its potential role as an ECG marker of increased arrhythmic risk. This is the first article to report the potential role of J-wave duration and slope as ECG markers of an increased arrhythmic risk. A delayed and prolonged J wave, marker of a transmural dispersion of repolarization, may represent the new discriminant able to distinguish between benign and malignant ER.