The purpose of the study was to investigate the possible role of autoantibodies in the development and type of left-ventricular hypertrophy (LVH). Three groups of subjects were studied:15 patients with hypertrophic cardiomyopathy (HCM; 11 males, 4 females; mean age 50.0 ± 16..3 years); (b) 15 patients with essential hypertension (10 males, 5 females; mean age 56.8 ± 13.5 years) with normal renal function and serum electrolytes and (c) 15 male athletes (mean age 20.8 ± 5.9 years). The control group consisted of 15 normal subjects with no sign of heart disease. The following indices of cardiac performance were determined by means of echocardiography: end-diastolic and end-systolic diameters, interventricular septum thickness, left-ventricular (LV) wall thickness, LV mass and LV mass index. The immunologic parameters studied included autoantibodies against (a) specific (anticardiac cell; ACA) and nonspecific (antimitochondrial cell; AMA) autoantigens according to a conventional indirect immunofluorescence technique. (1) Higher values for LV mass and LV mass index were observed in HCM. (2) The incidence of specific and nonspecific autoantibodies in hypertensive patients and in patients with HCM was significantly higher compared to athletes and controls. All ACA-positive individuals (5 with HCM, 3 with hypertension and 1 athlete) were AMA positive as well, while all ACA-negative individuals were also AMA negative. The ACA-positive individuals had higher C3c and C4 levels compared to the ACA-negative individuals. An autoantibody-mediated immunopathogenic role is discussed in the development and type of myocardial hypertrophy. Left-ventricular hypertrophy (LVH) due to heart disease (cardiomyopathies, hypertension or aortic stenosis) is considered as a pathological process followed by fibrosis and structural muscle changes [1]. On the contrary, LVH in athletes is considered as a ‘physiological’ myocardial response to exercise [2]. On the other hand, Autore et al. [3] have reported the presence of autoantibodies against mitochondria in patients with cardiomyopathies or hypertension with LVH, but not in athletes with LVH. These findings suggest the possibility that autoimmune mechanisms might be involved in the pathogenesis of LVH due to heart disease In this study we sought for the presence of autoantibodies against both specific and nonspecific antigens in athletes and patients with LVH of different origins, such as hypertrophic cardiomyopathy (HCM) or hypertension, in order to investigate the possible involvement of these autoantibodies in the development of LVH.