Routine moderate-intensity physical activity confers numerous cardiovascular benefits and reduces all-cause mortality. However, the health impact of exercise doses that exceed contemporary physical activity guidelines remains incompletely understood, and an emerging body of literature suggests that high levels of exercise may have the capacity to damage the cardiovascular system. This review focuses on the contemporary controversies regarding high-dose exercise and cardiovascular morbidity and mortality. We discuss the limitations of available studies, explore potential mechanisms that may mediate exercise-related cardiac injury, and highlight the gaps in knowledge for future research.