Abstract: AIM To investigate the effect of intracoronary injection high-dose tirofibann on the fragmented QRS complexes (fQRS) in patients with acute ST segment elevation myocardial infarction (STEM) after primary percutaneous coronary intervention (PCI). METHODS One hundred fifty acute STEMI patients enrolled continuously in the study were divided into high-dose tirofiban group (tirofiban group) and routine treatment group (routine group). The changes of fQRS on electrocardiogram and the MACE events were observed within 48 hours after primary PCI. RESULTS A total of 150 patients (aged 35-83 years; male, 82.7%) were included in the study and the baseline clinical characteristics were comparable between the two groups. Compared with patients in routine group, patients in the tirofiban group had lower levels of creatine kinase-MB ［(245±162) U/L vs. (311±180) U/L, P<0.05］ and corrected TIMI Frame Count (CTFC) post-PCI ［(23±7) vs. (30±10), P<0.05］, but higher left ventricular ejection fraction (LVEF) ［(51±6)% vs. (47±7)%, P<0.05］. The incidence of presence of fQRS on electrocardiogram in tirofiban group was lower than that in routine group (41% (30/75) vs. 57% (43/75), P<0.05). In Spearman’s correlation analysis, the level of CK-MB showed positive correlation with the number of leads with fQRS (r=0.207, P<0.05), but LVEF showed negative correlation with the number of leads with fQRS (r=-0.242, P<0.01). Multivariate analysis revealed that the intracoronary injection of high-dose tirofiban was the negative predictor of fQRS (Wald=4.257, OR: 0.364, 95% CI 0.139-0.95, P<0.05). There were differences in MACE events between the two groups during hospitalization, but the differences were not statistically significant (5.3% to 12%. t=3.63). CONCLUSION High-dose intracoronary injection of tirofiban can help to improve myocardial perfusion, reduce postoperative the presence of fQRS appearing on the standard 12-lead ECG and enhance cardiac functions.