The various ECG changes found in a group of 3,000 healthy athletes are discussed on the basis of eight representative ECG recordings. The common findings were sinus bradycardia, atrioventricular conduction disturbances, left and right ventricular hypertrophy according to the accepted voltage criteria, right axis deviation, intraventricular conduction disturbances (mainly in the right side of the heart), and various disturbances of the repolarization phase. The literature on this subject is reviewed, and the possible mechanisms involved in production of the various ECG changes are discussed. It is pointed out that in the absence of other evidence suggestive of cardiovascular disease, these changes should be considered as a normal variant and not lead to restriction of physical activity.