An increasing number of basic and clinical studies have suggested that the interval from the peak to the end of the electrocardiographic T wave (T(p-e)) may correspond to the transmural dispersion of repolarization and that amplification of the T(p-e) interval is associated with malignant ventricular arrhythmias. In this review, we outline the utility of the T(p-e) interval and the T(p-e)/QT ratio as an electrocardiographic index of arrhythmogenesis for both congenital and acquired ion channel disease leading to ventricular arrhythmias. In healthy individuals, the T(p-e)/QT ratio has a mean value of approximately 0.21 in the precordial leads and it remains relatively constant between the heart rates from 60 to 100 beats per minute. Interestingly, the T(p-e)/QT ratio is significantly greater in the patients at risk for arrhythmic event such as those with long QT syndrome, Brugada syndrome, short QT syndrome, and also in patients with organic heart disease such as acute myocardial infarction. Functional reentry is the underlying mechanism for arrhythmogenesis associated with an increased T(p-e)/QT ratio.