Abstract： Background Myocardial bridging (MB) as a congenital condition with a reported frequency of 5%-12% in diagnostic coronary angiography may be an important factor causing myocardial ischemia. However, its frequency in the infarct-related artery (IRA) of patients with ST-elevation myocardial infarction (STEMI) and the impact upon percutaneous coronary intervention (PCI) remain undetermined. In this study, we investigated MB frequency and its impact upon primary PCI in patients with STEMI.Methods The data of coronary angiography for 554 consecutive patients with STEMI who had undergone successful primary PCI were retrospectively analyzed to identify a frequency of MB in the IRA and its association with gender and age. According to the angiographic findings, the patients were divided into MB patients and non-MB patients. The endpoints of this study included immediate angiographic findings after primary PCI and 6-month major adverse cardiac events (MACE) (death, recurrent myocardial infarction, target lesion or vessel revascularization) between the MB patients and the non-MB patients.Results A frequency of MB in the IRA of 46 patients (8.3%) was identified in this series; it was more common in patients ≥65 years old (36/206) than in those <65 years old (10/348) (17.5% vs 2.9%, P<0.001). The trend of MB in the IRA was observed more frequently in women without significant difference than in men (10.2% vs 7.8%). TIMI grade III flow was achieved in 91.9% (509/554) of all patients following primary PCI, in 60.9% (28/46) of the MB patients and in 94.7% (481/508) of the non-MB patients respectively (P<0.001). The in-hospital mortality was 4.7% (26/554) in this series including 13.0% (6/46) of the MB patients and 3.9% (20/508) of the non-MB patients (P<0.001). A significant difference in 6 months MACE was seen between the MB patients (19%) and the non-MB patients (6.2%) (P<0.001). Conclusions MB in the IRA is relatively common in elderly patients with STEMI with a more evident trend in women, suggesting that arteriosclerosis and plaque rupture occurs more easily in the proximal artery to MB than in younger patients. Poor TIMI grade flow in patients with MB in the IRA after primary PCI may contribute to a high in-hospital mortality rate (13%) and 6-month MACE (19%) in the MB patients.