Abstract Background Proinflammatory stimuli induce a variety set of microRNAs (miRs) expressions in human mononuclear cells that regulate long pentraxin-3 (PTX3) gene, which associates with a procoagulant state in the endothelial cells. Purpose We evaluated, for the first time, the association of miR-224 and miR-155 expressions with coronary microvascular obstruction (MVO) and plasma PTX3 concentration in patients with acute ST-segment elevation myocardial infarction (STEMI) treated by primary angioplasty. Methods The expression levels of miR-224 and miR-155 on admission were evaluated in 217 consecutive patients with STEMI (symptom onset <12h) undergoing primary angioplasty between January 2018 and August 2018, and results were analyzed by the median values. The miRs expression and plasma PTX3 concentration were measured by TaqMan real-time PCR and human ELISA kit, respectively. The primary outcome of the study was the occurrence of angiographic MVO, defined as a post-primary angioplasty TIMI grade <3 flow or TIMI grade 3 flow with myocardial blush grade 0 or 1. Results After adjustment with sex, age and plasma PTX3 concentration, miR-244 ≥ median group was associated with angiographic MVO (odds ratio, 2.81; 95% confidence interval 1.34 to 5.92, p=0.006). Spearman analysis showed no correlations between miR-224 and miR-155 expressions with plasma PTX3 concentration. Conclusion This study suggests that miR-224 expression, (but not miR-155), associates with angiographic MVO following primary angioplasty for STEMI. However, miR-224 and miR-155 expressions did not correlate with plasma PTX3 concentration. Future studies are needed to find the molecular inflammatory pathway related with miR-224 expression in MVO. Funding Acknowledgement Type of funding source: None