INTRODUCTION: The Tpeak-Tend interval (TpTe) has been linked to increased arrhythmic risk. TpTe was investigated before and after primary percutaneous coronary intervention (pPCI) in patients with ST-segment elevation myocardial infarction (STEMI). METHOD: Patients with first-time STEMI treated with pPCI were included (n = 101; mean age 62 years; range 39-89 years; 74% men). Digital electrocardiograms were taken pre- and post-PCI, respectively. Tpeak-Tend interval was measured in leads with limited ST-segment deviation. The primary end point was all-cause mortality during 22 +/- 7 months (mean +/- SD) of follow-up. RESULTS: Pre- and post-PCI TpTe were 104 milliseconds [98-109 milliseconds] and 106 milliseconds [99-112 milliseconds], respectively (mean [95% confidence interval], P = .59). A prolonged pre-PCI TpTe was associated with increased mortality (hazard ratio, 10.5 [1.7-20.4] for a cutoff value of 100 milliseconds). Uncorrected QT and heart rate-corrected QT intervals (Fridericia-corrected QT) were prolonged after PCI (QT: 401 vs 410 milliseconds, P = .022, and Fridericia-corrected QT: 430 vs 448 milliseconds, P < .0001). CONCLUSION: In patients with STEMI undergoing pPCI, pre-PCI TpTe predicted subsequent all-cause mortality, and the QT interval was increased after the procedure.