Increased dispersion of QT interval in the 12-lead ECG have been proposed as risk factor of ventricular arrhythmias in post myocardial infarction (post-MI) patients, but its sensitivity and specifity is low for diagnosis and/or prognosis. We evaluate dispersion in other ventricular activity intervals, in order to determine whether they improve the separation between 15 normal subjects and 15 post-MI patients compared with QT dispersion. All the interval ventricular activity dispersions measured in the Frank's orthogonal leads (XYZ) are larger in post-MI patients than in normal subjects, but the differences are significant only for JTpeak (JTp) dispersion (p = 0.03). Therefore JTp dispersion could improve the identification of post-MI patients with risk of ventricular arrhythmias.