Regular moderate exercise training is effective for the prevention and treatment of many common chronic diseases and improves cardiovascular health and life expectancy. However, long-term excessive endurance exercise may induce pathological structural remodeling of the heart. The athlete's heart is characterized by enlargement of cardiac chambers and eccentric hypertrophy with preserved myocardial function as normal physiological adaptations for prolonged and intense endurance physical stress. However, recent studies have demonstrated transient right ventricular dysfunction and elevation of cardiac biomarkers following intense endurance exercise. Repeated bouts of acute stress may cause patchy fibrosis of the right heart and interventricular septum, creating an arrhythmogenic substrate. The following review summarizes the current medical literature on the effects of intense and prolonged endurance exercise on cardiac structure and function and its clinical significance.