The purpose of the study was to evaluate the early anatomic and functional changes of the left ventricles in junior freshman non-professional athletes just beginning specific regular training programs for 6 different types of sport. Forty-nine males (mean age 20 +/- 6 years) and 9 sedentary controls were studied by means of sequential M-mode echocardiograms, before and after a 10 to 12 week training period: 13 athletes started bicycle-riding (aerobic category), 6 sprint (anaerobic category), 6 weight-lifting (strength category), 13 soccer (mixed category), 11 rifle-shooting (manual dexterity category). Resting heart rate, blood pressure, left ventricular diameter (LVID), left ventricular posterior wall and interventricular septum thickness (LVPWT, IVST), left ventricular mass (LVMI), relative wall thickness (h/r ratio) and fractional shortening (FS%) of the LVID, cardiac index (CI) and stroke volume (SV) were comparable in all groups initially. After the training period, the cyclists, the sprinters and the soccer-players showed an increased LVID, LVMI and FS%. The cyclists and the soccer players also showed a decreased h/r ratio. The weight-lifters showed a slight increase of their LVMI, with an increased h/r ratio. We have, thus, documented that even after a relatively short non-strenuous training period, specific anatomical and functional changes occurred in the hearts of young athletes practising sports for recreational purposes, according to the type of sport.