Although moderate levels of exercise reduce cardiovascular morbidity and mortality in the general population, recent data have questioned whether higher doses of physical activity are associated with diminished health benefits and adverse outcomes. This review focuses on several issues at the center of this controversy including epidemiologic data describing mortality trends in those who engage in high levels of physical activity and recent observational data suggesting adverse cardiovascular outcomes among long-term endurance athletes. Specifically for the endurance athlete, the evidence and limitations of the available data associating veteran endurance athletes with an increased risk of atrial fibrillation, pathologic, and arrhythmogenic cardiac remodeling and accelerated coronary atherosclerosis will be discussed. This review will also provide practitioners involved in the care of athletes and highly active patients a conceptual framework for these contemporary controversies and will highlight key areas of uncertainty that will require future research.