The aim of the study was the scientific substantiation of new approaches to diagnostics, prognosis and treatment of patients with myocarditis on the basis of studying the peculiarities of development and progression of inflammatory heart damage, contractile function impairment, left ventricular (LV) remodeling and clinical course of heart failure (HF). A set of diagnostic criteria for acute myocarditis with a reduced LV ejection fraction (EF) was established as: the relationship of clinical manifestations with infectious-inflammatory process, the appearance of ventricular extrasystole >=1.0% and/or episodes of non-sustained ventricular tachycardia, decrease in the value of LV longitudinal global systolic strain =<7,0% and its velocity =<0,70 s-1, the presence of inflammatory changes of the myocardium in >=6,0 segments of the LV, the content of antibodies to cardial myosin >=3.0 opt. sq. units, Toll-like receptor type 4 expression >= 15.0 CIF and activity of myocardial induced lymphocyte blasttransformation >=7.0%. It was determined that the use of 6-month course of glucocorticoid therapy in addition to standard therapy of HF in patients with acute myocarditis is expedient for faster recovery of contractile capacity and reduction of end-diastolic LV volume, but does not affect the frequency of rhythm and conduction disorders in such patients, as well as the frequency of cardiovascular events during 24 months of follow-up. Using discriminant analysis, mathematical models have been developed for the early prediction of the adverse course of acute myocarditis: the presence of a reduced LV EF, II or higher HF functional class and persistence of non-sustained ventricular tachycardia after 12 months from the disease onset, as well as predicting mathematical model for the use of immunomodifying therapy, characterized by high sensitivity (76.2%) and specificity (79.4%). Predictors of cardiovascular events development in patients with acute myocarditis during the next 24 months from the clinical onset of the disease were identified as: level of LV EF =<30%; reduction of LV longitudinal global systolic strain =<7.0%; the presence of non-sustained ventricular tachycardia episodes, the presence of inflammatory changes in >= segments of the LV, the presence of delayed enhancement in >=5 LV segments in the 1st month from myocarditis onset. When conducting differential diagnosis of chronic myocarditis and dilated cardiomyopathy, the complex of the following diagnostic features should be taken into account: dilated cardiomyopathy, unlike chronic myocarditis, is characterized by the absence of immunopathological reactions activation except the presence of cardiospecific antibodies to beta1-adrenoreceptor and cardiac myosin, LV end-diastolic volume index >=110 ml/m2, decrease in LV circumferential and radial global systolic strain =<6.0 % and <=12.0 % respectively on the background of diffuse fibrotic changes in >=9.0 LV segments detected on cardiac MRI
