The purpose of the study was to compare the electrocardiogram wave pattern between athletes and non-athletes of elementary school children. Five 800m runners and five ordinary students partivipated in the study. In the first pahse of the study, the partivipants were exposed to physical examination. For the comparison of wave pattern , ST segment slope was also utilized, which shows myocardium hypertrophy, while the subjects exercised using Modified Bruce Protocol Mann - Whitney U signed rank test were used to analyse the mean rank between experimental group and controp group. There was significant mean rak difference in Heart Rate. R-R, P-R,T-R, However, no significant mean rank difference was found in QRS durations, Although electrocardiogram\'s amplitudes and ST segments slope had no significant mean rank difference athletes group showed more adaptation to exercise, thich meant left nventricle myocardium hypertrophy.