Background Shorter door-to-balloon (DTB) time in primary percutaneous coronary intervention (PCI) for ST-elevation myocardial infarction (STEMI) is associated with decreased mortality. Several strategies have been proposed to improve delay prior to arrival at the catheterization laboratory (Cath Lab). However, few strategies are available to expedite reperfusion in the Cath Lab. The aim of this study was to assess the impact of electrocardiogram (ECG)-directed culprit vessel PCI without performing complete coronary evaluation on DTB time in STEMI patients undergoing primary PCI. Methods A total of 223 consecutive STEMI patients who underwent primary PCI between Jan. 2009 and Dec. 2010 were included and compared according to procedural strategy in the Cath Lab. Under the discretion of operating physician, patients were underwent PCI of the culprit vessel as suggested by the ECG without undergoing full diagnostic coronary angiography (Group I, n=43) or after a complete diagnostic angiography (Group II, n=180). The primary outcome was Cath Lab arrival-to-balloon (CTB) time. Results There was no significant difference in baseline clinical and angiographic characteristics between the two groups. The CBT time (11 vs. 17 min, p=0.001) and DTB time (41 vs. 58 min, p<0.001) were significantly shorter in Group I than Group II. The rates of patients with DBT <90 min and <60 min were significantly higher in Group I than Group II (95.3% vs. 82.8%, p=0.037; 76.7% vs. 50.6%, p=0.002, respectively). In multiple linear regression analysis of 13 variables, ECG-directed culprit vessel PCI (棺=14.088, p=0.037) and CTB time (棺=1.15, p<0.001) remained significant independent predictors of DBT time. Conclusions This study showed that ECG-directed culprit vessel PCI reduced CTB time and DTB time significantly. Larger studies will be needed to determine whether broader utilization of this strategy results in beneficial outcomes.