Prolonged, strenuous exercise is associated with muscle injury; this may become permanent if there is insufficient time to rest between bouts of endurance exercise. We present here the experience of a 36 year old athlete who developed myocardial injury and pulmonary edema during a triathlon. Within 24-hours, after receiving furosemide 40 mg every 8 hours and oxygen, his pulmonary edema disappeared. The serum troponin became transiently elevated as it happens with a myocardial infarction but no electrocardiographic changes occurred. It is concluded that strenuous exercises may cause myocardial injury with a transient decrease of ventricular function and pulmonary edema. The possibility of some permanent damage cannot be excluded.