We studied 50 consecutive patients with relatively preserved systolic function (ejection fraction >40%, mean 53 +/- 11%) after acute myocardial infarction, and assessed indexes of dispersion of ventricular repolarization before and after a formal, phase II cardiac rehabilitation and exercise training program. After cardiac rehabilitation, statistically significant reductions occurred in QT dispersion, JT dispersion, and in the heart rate corrected indexes. These benefits add to the proven benefits of formal cardiac rehabilitation and exercise training programs and may reduce the subsequent risks of malignant ventricular arrhythmias and sudden cardiac death.