Sudden death prevention is one of the biggest challenges for the sport medicine.  As in general population, the majority of sudden deaths in athletes accounts for cardiac origin. The most effective way to prevent these events is the early diagnosis, during preparticipation screening, of the athletes with potentially lethal heart diseases and their disqualification for competitive sports. Standard 12-leads electrocardiogram plays an important role in this preventive activity. The present paper  intend to present the main normal and pathological changes on athlete's electrocardiogram. Even the usefulness of an electrocardiogram during the preparticipation screening is still controversial, this procedure allows the diagnosis for the majority of heart diseases responsible for sudden deaths in competitive athletes. A deep medical history and a complete physical examination, when added to the electrocardiogram, increase it's diagnostic value. As a conclusion of this paper, we could state that even if electrocardiographic abnormalities are found in less than 5% of the competitive athletes, this should not hinder the implementation of standard 12-leads ECG in the customary preparticipation screening.