This study analyzed the corrected QT dispersion (cQTd) before and at 24 hours after successful primary percutaneous coronary intervention (PCI) in 81 patients with single coronary artery disease and acute ST elevation myocardial in-farction. Major cardiovascular events (MACE) at 1 year were defined as death, nonfatal myocardial infarction, life-threatening arrhythmias, and heart failure hospitalization. The cQTd before primary PCI was significantly longer in patients without MACE than in patients with MACE (73.1 ± 29.3 versus 56.3 ± 25.2 msec, P = 0.026). The cQTd at 24 hours after primary PCI was significantly shorter in patients without MACE than in patients with MACE (38.4 ± 20.8 versus 50.8 ± 28.7 msec, P = 0.045). Thus, the absolute cQTd change was significantly higher in patients without MACE compared to patients with MACE (P = 0.001). By multivariate analysis, absolute cQTd change was an independent predictor for the development of MACE, with an odds ratio of 1.498 for each 10-msec decrement in absolute cQTd change (95 percent confidence interval, 1.157 to 1.939, P = 0.002). In conclusion, the absolute cQTd change after primary PCI was an independent predictor of the development of MACE in patients with single vessel disease and acute ST elevation myocardial infarction.