This study was carried out on 43 patients affected by dilated cardiomyopathy to investigate some of the etiopathological hypotheses on this illness. The Authors investigated: the persistence of virus genoma (coxsackie, HBV) on endomyocardial biopsies; the pattern of the II class major histocompatibility complex (MHC) were in the blood lymphocytes; the microvascular aspect of coronary circulation in the endomyocardial biopsies. Finally, in a separated group of 19 patients, the microvascular circulation was studied on skin biopsies and correlated with diabetic, valvular and normal subject. The results showed a 14% positivity for the presence of the virus genoma and a significant predominate of DR5 in the II class MHC of patients with a worse ventricular function. Capillary vessels of the coronary microcirculation were dilated in the 48% of the patients, especially in more compromised subjects. Viral myocarditis seem to play a role in the etiopathogenesis of dilated cardiomyopathies (DCM) and the pattern of MHC could influence the progression of the illness. The microcirculation is probably a pathophysiological aspect. No etiological hypothesis seems to predominate.