The aim of the study was to assess whether trimetazidine (TMZ) could affect dispersion of atrial depolarization and ventricular repolarization. Corrected QT interval (QTc), QTc dispersion (QTc-d), Tpeak-Tend, and Tpeak-Tend dispersion (Tpeak-Tend-d) were measured in 30 patients with chronic heart failure (CHF) before and 6 months after randomization to conventional therapy plus TMZ (17 patients) or conventional therapy alone (13 patients). After 6 months, QTc was significantly reduced in both groups, whereas QT-peak was increased only in control group. Tpeak-Tend-d decreased (from 63.53 +/- 24.73 to 42.35 +/- 21.07 milliseconds, P = .006) only in TMZ group. When subgrouped according to CHF etiology, only ischemic patients on TMZ showed Tpeak-Tend-d reduction (65.00 +/- 27.14 vs 36.67 +/- 11.55 milliseconds, P = .001 in ischemic patients; 60.00 +/- 20.00 vs 56.00 +/- 33.86 milliseconds, P = NS, in nonischemic). These electrophysiological properties indicate an undiscovered mechanism of action of TMZ, which could be useful in conditions at risk of major arrhythmias.