Rhythm disorders represent the main challenge for the sport physician and cardiologist to grant the certificate of sports eligibility to the athletes. Arrhythmias that occur in athletes can be divided into two types. The most common are generally an expression of morphofunctional changes in the athlete's heart and are represented by certain forms of non-complex tachyarrhythmias and bradyarrhythmias. On the other hand you may encounter less frequently more complex arrhythmias that may be an epiphenomenon of cardiomyopathy can cause sudden death during sports activities. By collection of detailed medical history, careful examination, and in particular by the 12-lead electrocardiogram is already possible to understand the arrhythmic risk sporting population. After an analysis of main types of arrhythmias encountered in the athlete and the main diagnostic methods, this study focuses on the interplay between forms of arrhythmias, arrhythmogenic heart diseases and activity sports. Surely the increased adrenergic tone and anatomical and functional alterations sports-related favor the development of arrhythmia and sudden death risk in structural cardiomyopathies. But this is not yet resolved the question of whether sport is able to increase the incidence of ventricular arrhythmias in a normal heart. Dangerousness of the arrhythmia is variable depending on the sport is practiced with high intensity or not. Even if it is important considering the possibility of syncope in hazardous environments. Arrhythmias at risk impose the exclusion of the athlete from the practice of sport. In some cases it may be considered a drug treatment, ablation, and in rare and selected cases, the implantation of a pacemaker or an implantable defibrillator.