ST-elevation myocardial infarction (STEMI) results from acute thrombotic obstruction of a coronary artery. Percutaneous coronary intervention (PCI) is the treatment of choice to restore blood flow. The incidence of guidewire-induced reopening of the infarct-related coronary artery (IRA) and its association with post-procedural TIMI flow and long-term mortality were assessed. Angiograms of consecutive STEMI patients admitted to the catheter laboratory of the Medical University of Vienna between January 2003 and December 2005 were analysed. TIMI flow was graded prior to and after guidewire insertion into the distality of the IRA, and at the end of the procedure. Initial TIMI 0 flow was present in 476 (47.0%) of 1,012 cases. Target vessel reopening after guidewire insertion defined as any flow >TIMI 0 flow occurred in 150 patients (37.2%), and was associated with improved survival after a median of 914 (609-1,238) days (p=0.017). Reflow after guidewire insertion was an independent predictor of post-procedural TIMI flow (odds ratio=3.10, 95% confidence interval [CI]=1.64 - 5.86], p<0.001) and mortality (hazard ratio=0.51, CI=0.28 - 0.94], p=0.029). Target vessel reopening by guidewire insertion is a new predictor of prognosis. Target vessel flow after guidewire insertion should be assessed in a standardised fashion during PCI.