Electrocardiography occupies a special place among a significant list of other methods for diagnosing the pathology of the cardiovascular system of athletes. Often its results differ significantly from those in the general population, being a consequence of the adaptation of the heart to economical functioning at rest and super-intensive work in training and competitions. This review focuses on the features of the “athlete's electrocardiogram (ECG).” In particular, those changes that are not a reason for removing athletes from physical activity, but in combination with known factors can lead to more serious changes up to sudden cardiac death. Fatal rhythm disorders in athletes are described, possible in Wolff-Parkinson-White syndrome, syndrome of ion channel pathology, arrhythmogenic dysplasia of the right ventricle, etc. Particular attention is paid to arrhythmia due to connective tissue dysplasia syndrome. Knowledge of these issues is necessary to choose the right tactics for an athlete with changes to the electrocardiogram and in the protocol of daily Holter monitoring of the electrocardiogram, and a doctor related to sports medicine should be aware of the features of “electrophysiological remodeling” of the athlete's heart, normal and pathological “sports electrocardiogram,” about conditions accompanied with the development of serious rhythm disorders and algorithms for examining the cardiovascular system of the athlete.