Major adverse cardiac events in endurance exercise are usually due to underlying and unsuspected heart disease. The investigators present an analysis of major adverse cardiac events that occurred during 2 consecutive annual long distance races (a 36-km beach cycling race and a 21-km half marathon) over the past 5 years. All patients with events were transported to the hospital. Most of the 62,862 participants were men (77%; mean age 40 years). Of these, 4 men (3 runners, 1 cyclist; mean age 48 years) collapsed during (n = 2) or shortly after the races, rendering a prevalence of 0.006%. Two patients collapsed after developing chest pain, 1 of whom needed resuscitation at the event site, which was successful. These patients had acute myocardial infarctions and underwent primary angioplasty. The third patient was resuscitated at the site but did not have coronary disease or inducible ventricular tachycardia or ventricular fibrillation and collapsed presumably because of catecholamine-induced ventricular fibrillation. The fourth patient experienced heat stroke and had elevated creatine kinase-MB and troponins in the absence of electrocardiographic changes. In conclusion, the risk for major adverse cardiac events during endurance sports in well-trained athletes is very low.