Funding Acknowledgements Type of funding sources: Public Institution(s). Main funding source(s): A.L. Myasnikov Institute of Clinical Cardiology, Russian Cardiology Research and Production Complex, Ministry of Health of Russia, Moscow, Russia Background A growing number of publications describe the role of cardiac MRI in STEMI prognostic assessment. Infarct size, microvascular obstruction (MVO) and myocardial heterogeneity are among the most prognostically significant MRI parameters in MI. Primary PCI (pPCI) is the current standard of STEMI treatment. The impact of clinical factors on the development of MVO, myocardial heterogeneity and infarct size remains insufficiently investigated. Purpose To investigate the impact of certain medical history aspects, clinical and laboratory parameters on the most prognostically significant MRI measures of acute MI (MVO, infarct size, myocardial heterogeneity). Methods The study included 52 patients with first STEMI within <48 hours of onset. All patients urgently underwent coronary angiography with pPCI of infarct-related arteries (IRA). On Days 3-7 contrast-enhanced cardiac MRI was done. Tissue analysis of scans was performed using CVI 42 software evaluating infarct size, MVO, myocardial heterogeneity, and left ventricle (LV) ejection fraction (EF). Results 85% patients were men, with mean age of 59.09 ± 7.7 years. All patients underwent pPCI for reperfusion. The median time from symptom onset to pPCI was 3 hours.  We analyzed the influence clinical and laboratory factors impacting cardiovascular prognosis on the development of MVO, infarct size, and myocardial heterogeneity. Odds ratios demonstrated no significant relationship between arterial hypertension (OR 2.10, CI 0.57-7.79 р=0,2), smoking (OR 1.01 CI 0.32-3.20, р=0.9), obesity defined as BMI >30 kg/m2) (OR 0.83 CI 0,50-1.39, р=0.16) and MVO development. However, diabetes mellitus had significant effect on MVO development (OR 4.34 CI 1.34-14.03, р=0.01). With regards to laboratory parameters, relationship between hs-Troponin elevation > >8400 pg/mL and MVO occurrence (OR 7.00, CI 0.79 – 61.74, р=0.04). Correlation analysis demonstrated association between myocardial heterogeneity and BNP (r 0.612, р<0.0001), as well as advanced age (r 0,544, р<0,0001). Inverse correlation was found between myocardial heterogeneity and LV EF (r -0.461, р=0.0006). We also analyzed the factors associated with infarct size and found correlation between this parameter and BNP levels (r 0,553, p = 0,0003), as well as MVO magnitude (r 0,383, p = 0,005). Inverse correlation was found between infarct size and history of hypertension (r -0.380, p = 0.0054) Conclusions Type 2 diabetes mellitus, was found to be an independent predictor of microvascular obstruction on MRI. Elevation of hs-Troponin >8400 pg/mL was found to be associated with MVO development. Correlation data analysis demonstrated that high BNP may indicate higher infarct size and myocardial heterogeneity values (r 0.612, р<0.0001).