• Arrhythmic right ventricular dyplasia
• atrial arrhythmias
• exercise training
• left ventricular hypertrophy

The cardiovascular benefits of regular exercise of moderate intensity are well established. Indeed, when one considers the burgeoning epidemic of childhood obesity and its associated complications, exercise may be regarded as the most clinically and cost effective prescription dispensed by healthcare professionals. The potential hazards of more intensive exercise are occasionally highlighted by the sudden cardiac death of an individual during or immediately after exercise; however, such catastrophes are extremely rare, largely striking young athletes harboring inherited or congenital arrhythmogenic substrates including primary cardiomyopathies, accessory pathways and ion channelopathies, and older athletes with advanced coronary atherosclerosis.1 Despite the emotive visibility afforded by these deaths in the media, the positive reputation of exercise remains unscathed by the fact that exercise is regarded as a mere trigger for arrhythmia in a small proportion of predisposed individuals but never directly incriminated in the pathogenesis of the fatal substrate.

However, the past two decades have witnessed an extraordinary and engaging sporting milieu where humanly achievable physical targets during competition appear infinite, being reflected by arduous training schedules involving several hours of intensive exercise each day among the most competitive athletes. In parallel, there has been an escalation in the number of individuals repeatedly participating in grueling ultra-endurance events including the marathon, triathlon and the “iron man”, which bear no resemblance to the moderate levels of exercise recommended for cardiovascular benefits. Whereas participation of lifelong moderate exercise is of undoubted therapeutic value, participation in exceedingly intensive and prolonged episodes of exercise associated with sustained increases in cardiac preload and afterload and high concentrations of circulating catecholamines, inevitably raise the issue of the potentially detrimental effects of chronic intensive exercise in an otherwise normal heart.

Such concerns may not be without pertinence as several studies in athletes participating in ultra-endurance events have demonstrated increased blood …