Abstract: Objective To observe the effects of percutaneous coronary intervention (PCI) on QT dispersion (QTd) and explore its clinical significance in patients with acute myocardial infarction (AMI). Methods The electrocardiograms recorded before and one day after PCI were analyzed in 138 patients with AMI. The duration from the onset of AMI to PCI operation was less than 6 h in 72 patients and 6 to 12 h in the other patients. All the patients underwent emergency percutaneous transluminal coronary angioplasty and subsequent coronary stenting. QT intervals, QTd, and heart rate-corrected QT intervals (QTc) and QTd (QTcd) were measured and calculated. Results In both patient groups receiving PCI with delay shorter and longer than 6 h after AMI, QT and QTc after PCI were not significantly different from that before PCI, but the QTd and QTcd were remarkably decreased after PCI (all the P values <0.01). Moreover, the QTd and QTcd in the patients with delay of PCI less than 6 h were significantly shorter than those in patients the with greater-than-6-hour delay (P<0.05), and the inhospital mortality was 4.2% and 7.6% in the two groups, respectively (P=0.394). Conclusion Successful PCI may notably reduce QTd in the patients with AMI, whose earlier performance usually produces better effects.