BACKGROUND To investigate the relationship between the presence of fragmented QRS (fQRS) on electrocardiogram (ECG) and plasma NT-proBNP levels in patients with ST-elevation myocardial infarction (STEMI) who underwent primary percutaneous coronary intervention (PCI). The in-hospital prognostic value of the presence of fQRS was also assessed. METHODS In this retrospective study, 216 patients with STEMI who were undergoing primary PCI were included. fQRS was identified in ECG following primary PCI. The fQRS included various morphologies of the QRS (< 120 ms), which included an additional R wave (R') or notching in the nadir of the S wave, or > 1R' (fragmentation) in 2 contiguous leads, corresponding to a major coronary artery territory. N-terminal pro-brain natriuretic peptide (NT-proBNP) levels were measured immediately, 24 and 48 hours after admition and the peak level was adopted. Patients were divided into two groups based on the presence (n = 126) or absence (n = 90) of a fQRS on ECG. RESULTS NT-proBNP level was found to be significantly higher in fQRS (+) group compared to the fQRS (-) group (p < 0.001). The in-hospital advanced heart failure were found to be significantly more frequent in the fQRS (+) group. In logistic regression analysis, the fQRS ≥ 3 leads, fQRS in anterior leads, and NT-proBNP were independently related with in-hospital major adverse cardiac events that includes cardiovascular mortality, reinfarction, advanced heart failure, repeat target vessel revascularization, ventricular arrhythmias, atrioventricular block or sroke in the hospital. The area under the curve using the NTpro-BNP level for the prediction of fQRS was 0.809. CONCLUSIONS The presence of fQRS is significantly associated with NT-proBNP and left ventricular ejection fraction, which can predict left ventricular function in patients with STEMI. fQRS is a prognostic marker of impaired regional ventricular systolic function.