Aim To elucidate the effects of percutanious coronary intervention (PCI)on QT dispersion (QTd)and to find out its clinical significance. Methods The electrocardiograms recorded before and one day after PCI in 138 patients with acute myocardial infarction (AMI)were analyzed. The duration from the onset of AMI to PCI operation was less than 6 h in 72 patients and 6 to 12 h in others. All the patients underwent emergent and subsequently coronary stenting. QT intervals, QTd, and heart-rate-corrected QT intervals (QTc) and QTd (QTcd)were gauged and calculated. Results In both the less-than- and the longer-than-6-hour group, QT and QTc after PCI were not significantly different from before PCI. But the QTd and the QTcd after PCI were remarkably decreased(all p<0.01). Moreover, the QTd and QTcd in the less-than-6 h group were significantly shorter than those in the longer-than-6 h group (all p<0.05). And the inhospital mortality was 4.2% and 7.6%,respectively (P=0.394). Conclusions Successful PCI could notably reduce QTd in patients with AMI. The earlier the PCI was performed,the better the effects of reperfusion by PCI on reducing QTd.