Atrial fibrillation (AF) is the most common cardiac arrhythmia in athletes. Epidemiological studies have documented a greater prevalence of AF in athletes engaged in long-term endurance sports. Several mechanisms were proposed to underlie the association between exercise and AF, but the exact pathophysiology remains unclear. The studies up to now have been concentrated on the competitive middle-aged endurance athletes, but there is no evidence of AF prevalence among highly active noncompetitive athletes of the same age. Endurance athletes who do not compete might be at a lower risk for AF than their competitive peers. This hypothesis is theoretically examined, and the current evidence summarized in this article.