Increased QT dispersion (QTd) is a marker of myocardial electrical instability and predicts ventricular arrhythmias and sudden cardiac death. Exercise training (ET) has been shown to reduce both QTd and cardiovascular mortality in various populations. Patients with metabolic syndrome (MS) have been shown to have increased QTd. The effect of ET on QTd in MS patients however is unknown. We sought to assess the effect of a long-term (> or = 6 months) ET program on QTd parameters in MS patients with and without coronary heart disease (CHD). Fifteen CHD and 31 non-CHD patients with MS (mean age, 64 +/- 7 and 57 +/- 9 years, respectively) were identified at entry into identical ET programs. MS was defined using modified National Cholesterol Education Program criteria. A control group consisted of 8 MS patients with CHD (mean age, 65 +/- 6 years). Ventricular repolarization (QT dispersion = QTd, standard deviation of QT = SDQT, relative dispersion of QT = RDQT, QT corrected dispersion = QTcd), metabolic and exercise parameters were measured before and after ET. Program duration was over 9 months (312 +/- 100 versus 284 +/- 101 days in CHD and non-CHD cohorts, P = NS). QTd decreased in both ET groups (QTd pre versus post = 66 versus 56 ms in CHD group, P < 0.01; 58 versus 51 ms in non-CHD group, P < or = 0.01). Other ventricular repolarization parameters also improved significantly in both MS groups following ET, but remained unchanged in the control group. A long-term ET program improves QTd in patients with MS with and without CHD.