The object of the study was to investigate possible myocardial adaptations to intensive body building training and to differentiate them from the athlete's heart resulting from high intensive endurance training. Seven top-level body builders (BB) were examined by one- and two-dimensional echocardiography and bicycle ergometer step test. They were compared with seven highly endurance-trained athletes (E) using the matched pair procedure. BB showed normal blood pressure at rest and during ergometric exercise; their ergometric performance was in the normal range of sedentary subjects. Absolute left ventricular muscle mass (LVMM) as well as one-dimensional measurements of wall thickness and internal diameters were found to be similar in BB and E, while body weight and surface-related values were clearly higher in E. The ratios between LV myocardial thickness and internal diameter (M-mode) as well as between LVMM and LV volume (combined one- and two-dimensional method) were not statistically different between BB (0.356 ± 0.077 and 1.10 ± 0.16) and E (0.436 ± 0.062 and 1.26 ± 0.21). LV contractility was similar in both groups. Diastolic parameters showed only a slight tendency toward slower isovolumetric relaxation in BB. A significant correlation existed between lean body mass and LVMM in BB but not in E. The findings suggest that intense body building over a period of several years does not induce any form of concentric hypertrophy. Analogously to the increase in body dimensions, body building also causes an increase in heart size with an unchanged mass/volume ratio. There is no evidence of an enlargement of the heart in relation to body weight as occurs in endurance athletes.