Long-term pursuit of endurance sport: a new risk factor for atrial fibrillation? Lone atrial fibrillation is a term used when the arrhythmia develops in patients under 60 years old without any underlying cardiovascular disease. The aetiology is currently unknown but some recent data suggest that there is an association between a life-long practice of the endurance sport and atrial fibrillation. Long-term structural changes in the left atrium and increased vagal tone related to high intensity training are the main hypothesized mechanisms. The best therapeutic approach is still unknown but radiofrequency catheter ablation can become the treatment of choice for this kind of patient.