The purpose of this article is to discuss the dilemmas in differential diagnosis of myocarditis and dilated cardiomyopathy of different etiologies. According to the definition of the WHO and the ISFC the dilated cardiomyopathy is a myocardial disease recognized by the severe enlargement of the left and/or the right ventricle causing the decrease in systolic function of the heart (decrease of contractility) with the development of congestive heart failure. In order to distinguish primary cardiomyopathies defined as a muscle heart disease sui generis on the one hand from cardiomyopathies as the outcome of chronic inflammatory myocarditis (chronic persistent myocarditis, chronic immune myocarditis, chronic viral heart disease) on the other hand, it is necessary to follow a complicated diagnostic flow diagram. Methods that are to become routine in diagnostic procedure are described. Etiologic diagnosis of dilated cardiomyopathies is not possible without heart muscle biopsy. The bioptic specimens must be analyzed using light microscope (according to Dallas criteria), electron microscope, and afterwards immunohistologically and immunohistochemically (in situ hybridization). The total result of these investigations leads to the final conclusion about etiological diagnosis of dilated cardiomyopathy. The directions in the treatment of dilated cardiomyopathies and acute myocarditis are stated, as well as the importance of immunosuppressive therapy in these conditions. In the treatment of acute myocarditis digoxin should be avoided and other inotropic substances used instead.