In the present study we evaluated the importance of autoimmune mechanisms in dilated cardiomyopathies. Sera from 81 patients with dilated cardiomyopathy, 17 patients with various other cardiologic diseases and 40 apparently healthy blood donors were tested with an immunoassay method for the presence of autoantibodies against tropomyosin, myosin and actin, three antigens which are components of the cardiac tissue. Elevated values of autoantibodies were obtained in a high percentage of patients with dilated cardiomyopathy as compared to the control group (66% antitropomyosin IgG, 66% antimyosin IgG, 28.3% antitropomyosin IgM). It has also been shown, for the first time, that patients with dilated cardiomyopathy and positive for at least one of the screened autoantibodies had a thicker interventricular septum thickness, systolic and diastolic than patients negative for the presence of autoantibodies (1.18 +/- 0.3, 1.2 +/- 0.3 vs 0.88 +/- 0.1, 0.9 +/- 0.2 respectively), a finding that indicates the importance of these autoantibodies. Although further investigation is needed, it is concluded that the detection of these autoantibodies can be a useful tool for the diagnosis, follow-up and prognosis of the patients with dilated cardiomyopathy.