BACKGROUND The aim of this study was to analyze the relative expression level of miR-30d-5p, miR-23a-3p, and miR-146a-5p, and to comprehensively assess the diagnostic and predictive possibilities of these miRNAs. Their expression changes have not yet been sufficiently investigated during acute myocardial infarction. Therefore, it is important to comprehensively assess the diagnostic and predictive possibilities of these micro-ribonucleic acids (miRNAs). MATERIAL AND METHODS Random patients with ST‑elevated myocardial infarction (STEMI) were enrolled into the study group. The control group was comprised of patients with no inflammation or ischemic heart disease who were hospitalized for minor elective surgery. The relative expression level for each miRNA was determined by reverse transcription quantitative polymerase chain reaction (RT-qPCR)-analysis. RESULTS There were 88 participants enrolled into the study: 62 patients were diagnosed with STEMI and there were 26 healthy controls. Expressions of miR-30d-5p, miR-146a-5p, and miR-23a-3p were respectively 1.581-fold, 4.048-fold, and 4.857-fold lower in patients with STEMI compared to the control group patients (all P values were <0.001). Downregulation of miR-23a-3p was significantly negatively correlated with risk scores of GRACE (Global Registry of Acute Coronary Events) and APACHE II (Acute Physiology and Chronic Health Evaluation II). MiR-23a-3p was a fair predictor for STEMI: area under the curve (AUC)=0.806. Cox regression analysis revealed that expression levels of analyzed miRNAs were not significantly associated with negative endpoints at 1 month after the onset of STEMI. CONCLUSIONS All investigated miRNAs were differentially expressed when comparing patients with STEMI and control group individuals. The evaluation of miR-23a-3p expression levels in serum could be useful to assess the severity of STEMI and as a potential diagnostic biomarker of this condition. In addition, miR-23a-3p may provide limited short-term prognostic value for STEMI patients.