Regular physical activity has a positive impact on general health and well-being. The volume and the intensity of training undertaken by competitive athletes, particularly those engaging in endurance sports, including the triathlon, is between 10- to 20-fold higher than the current recommendations for the general population. Such athletes develop a constellation structural and functional adaptations within the heart ("athlete's heart") that permit the generation of a large and sustained increase in cardiac output for prolonged periods and also impact on the surface 12-lead ECG. Sinus bradycardia, first-degree atrioventricular (AV) block, voltage criteria for ventricular hypertrophy and incomplete right bundle branch block are common electrical manifestations in endurance athletes. Up to 50% of endurance athletes have a ventricular cavity dimensions that exceed the upper limit of normal, and a proportion of large males may reveal a left ventricular end diastolic diameter >60 mm. Occasionally structural adaptations may overlap with those observed in individuals with cardiomyopathy. Sudden death is a very rare event in triathlons but usually affects males and most commonly occurs in the swim section. Deaths may be due to an inherited or genetic cardiac abnormality in young (<35-year-old) athletes and atherosclerotic coronary artery disease in older athletes. The impact of life-long participation in endurance exercise on an otherwise normal heart is unclear, but there is emerging evidence that male endurance athletes who have been competing for several years have a higher prevalence of atrial fibrillation. A small proportion of studies have also shown a higher prevalence of myocardial scar.
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