There is controversy about the influence of QT dispersion on the incidence of early ventricular arrhythmias in patients with acute myocardial infarction (AMI). The QT and QTc dispersion (QTd, QTcd) between two groups of patients with AMI were compared: 39 patients with early sustained ventricular tachycardia or ventricular fibrillation (VT/VF) and 40 patients without such arrhythmias. QTd and QTcd were calculated from the admission and predischarge ECG, expressed as the difference between the maximum and minimum QT and QTc interval in 12 leads. The coefficient of variability was also calculated (VQT, VQTc). Groups did not differ significantly in age, incidence of previous infarction, Killip class, electrolyte status, infarct location, expected and final ECG infarct size, enzymatic infarct size, thrombolytic treatment and reperfusion rate, i.e., in variables that could influence the VT/VF occurrence. On admission, patients with VT/VF had significantly greater QTd (77+/-23 vs 53+/-27 ms, P<0.001) and QTcd (90+/-29 vs 62+/-28 ms, P<0.001); VQT and VQTc were also significantly higher. Although similar differences existed on predischarge ECG, they were smaller. The results indicate that QT dispersion varies during the illness, and that measurements of QT dispersion could be helpful in predicting serious ventricular arrhythmias.