Cardiac arrhythmias are among the most important causes of non-eligibility to sports activities, and may be due to different causes (cardiomyopathies, myocarditis, coronary abnormalities, valvular diseases, primary electrical disorders, abuse of illicit drugs). The list of illicit drugs banned by the International Olympic Committee and yearly updated by the World Anti-Doping Agency includes the following classes: stimulants, narcotics, anabolic agents (androgenic steroids and others such as beta-2 stimulants), peptide hormones, mimetics and analogues, diuretics, agents with an antiestrogenic activity, masking agents. Almost all illicit drugs may cause, through a direct or indirect arrhythmogenic effect, in the short, medium or long term, a wide range of cardiac arrhythmias (focal or reentry type, supraventricular and/or ventricular), lethal or not, even in healthy subjects with no previous history of cardiac diseases. Therefore, given the widespread abuse of illicit drugs among athletes, in the management of arrhythmic athletes the cardiologist should always take into consideration the possibility that the arrhythmias be due to the assumption of illicit drugs (sometimes more than one type), especially if no signs of cardiac diseases are present. On the other hand, in the presence of latent underlying arrhythmogenic heart disease including some inherited cardiomyopathies at risk of sudden cardiac death, illicit drugs could induce severe cardiac arrhythmic effects.