At this year’s Birkebeiner ski marathon, 12,000 cross-country skiers will line up for the 54 kilometer race, run almost every year since 1932. In 1976 almost 150 participants were invited to take part in a long-term study designed to discover the extent of latent heart disease in these elite cross-country skiers. Now, the results of the follow-up study have been published and suggest that long-distance competition skiers are at an unusually high risk of atrial fibrillation.