The aim of the study: to evaluate the efficacy of the intravenous 5-lipoxygenase inhibitor quercetin for the prevention of microvascular obstruction (MVO), intramyocardial hemorrhage (IMH) and reperfusion myocardial injury in timely revascularized patients with STEMI. Methods. We examined 37 patients with the first acute anterior STEMI who were admitted in the first 6 hours after symptoms onset. Patients were divided into two groups: group 1 — 18 patients, who in addition to standard acute myocardial infarction therapy were treated by intravenous quercetin (Corvitin®, PJSC SIC «Borshchahivskiy CPP», Ukraine) and group 2 — 19 patients with standard therapy. Magnetic resonance imaging (MRI) was performed on day 3–4 and 3 months after STEMI development on a «Vantage Titan 1.5T» MR tomograph («Toshiba», Japan) in standard projections. The presence of MVO was assessed in the early gadolinium enhancement (EGE) phase, and T2-weighted images were used to detect IMH. The area of myocardial infarction (postinfarction fibrosis) was assessed in late gadolinium enhancement phase in 90 days. Results. The signs of MVO in the phase of EGE on day 3–4 were detected in 22 (91.7%) of 24 patients (p>0.05, when compared between groups). IMH was determined in 9 (37.5%) patients: 1 (11.1%) patient in quercetin group vs 8 (53.3%) patients in control group; p=0.024. No significant difference in the final size of myocardial infarction (postinfarction fibrosis zone) according to cardioMRI after 3 months of follow-up between patients of the two groups was detected. Conclusions. Addition of intravenous quercetin (started before revascularization) to standard baseline myocardial infarction treatment was associated with a reduced likelihood of IMH development after primary percutaneous coronary intervention in patients with STEMI.