Introduction: Athletes often exhibit benign structural and electrical remodelling of the heart as a physiological adaptation to regular and sustained physical training. Cardiovascular examination of athletes (including ECG monitoring) is performed to take information about influence of physical activity on the functional conditions of circulatory system, and to identify underlying heart disease (especially in aspect of prevention of sudden cardiac death) requiring the extension of diagnostic workup. Aim of the study: The aim of this study was to evaluate changes in resting electrocardiograms in 14-year-old athletes. Materials and methods: Resting ECGs were assessed in 28 adolescents (14 boys and 14 girls) aged 14 years beginning education in sports lower secondary school of athletic profile. Results: The most common ECG changes among adolescent athletes after long-term physical training were: sinus bradycardia and sinus respiratory arrhythmia. The Sokolow-Lyon voltage criterion for left ventricular hypertrophy was fulfilled in 4 cases (in initial ECG in 10 cases) and for right ventricular hypertrophy – in 3 cases (in initial ECG in 9 cases). 16 athletes had signs of early repolarisation, usually in lateral leads. Conclusions: Changes in resting electrocardiograms in young athletes (especially sinus bradycardia, sinus respiratory arrhythmia, early repolarisation) are a result of physiological adaptation to exercise. Dynamic exercise seemed to reduce amplitudes of R and S waves in right and left precordial ECG leads and increase amplitude of T waves. The ECG can provide valuable information about electrical changes that are a result of regular training.