The purpose of the research was to look for additional laboratory markers and instrumental parameters associated with persistence of left ventricular (LV) systolic dysfunction and heart failure (HF) in acute diffuse myocarditis (ADM), and studying the possibilities of predicting the course of the disease after 12 months of follow-up. We examined 38 patients with ADM – 25 men and 13 women in the first month from the onset of the disease, after 6 and 12 months of follow-up. After 12 months 32 patients that survived were divided into 2 groups: 1st group – 17 patients with preserved systolic function – LV ejection fraction (EF) > 45 %, HF NYHA class ≤ I, 2nd group 15 patients with systolic dysfunction – LV EF ≤ 45 %, HF NYHA class ≥ II. In all patients we studied venous peripheral blood with measurement of antimyocardial antibody titers and blast-transformation lymphocyte activity against myocardium (BTLAm). In the supernatants of mononuclear cells we studied concentrations of the following cytokines: tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), interleukin-2, interleukin-10 and interferon-γ. Additionally in serum we measured the activity of catalase and superoxidedysmutase. Echocardiography was performed with assessment of the indexes of LV end-diastolic volume, end-systolic volume and EF. Cardiothoracic index was measured by chest roentgen. Inflammatory cytokine concentrations on the 1st month after the ADM onset were higher than those after 6 months and appeared on average: for IL-1β 156.8±16.3 and 91.8±13,4 pg/ml (Р<0.05) respectively, for TNF-α 214.2±28.1 and 163.3±20.1 pg/ml (Р<0.05) respectively, and the BTLAm activity on the 1st month in comparison with the 6 months period was also higher: 6.90±0.52 and 4.90±0.51 % (Р<0.01) respectively. Activation of immunopathologic reactions and antioxidant enzyme activity depression at onset of the disease was accompanied by LV dilatation and systolic dysfunction. We built the prognostic model for the assessment of probability of LV systolic dysfunction at the first month after the disease onset and HF preservation after 12 months of disease course. In conclusion, LV dilatation and impairment of its systolic function is associated with activity of immune response and oxidative stress. We detected the most informative laboratory and instrumental markers which are useful for prediction of myocarditis course and built the prognostic model with high sensitivity and specificity.