Triathletes, like all athletes engaged in sustained physical activity, generate body heat through well-described energy processes. And when these phenomena are compounded by environmental factors such as heat loading, thermoregulatory mechanisms are seriously challenged and innate mechanisms of heat dissipation are rapidly invoked. Elevated core body temperature is the inevitable outcome of impaired thermoregulation and when this maladaptation persists, the consequences may be catastrophic. Most authorities agree that unrecognised heat-related illness proceeds along a continuum from seemingly trivial heat cramps through heat exhaustion to heat stroke, with attendant life-threatening consequences reflective of a core temperature exceeding 40 °C. While this progression is not inevitable, early intervention affords protection to the vulnerable athlete and reduces the possibility of serious systemic sequelae. Prolonged exertional heat stress has the potential for multi-organ failure via a pathophysiological cascade initiated at a cellular level. Several international sports federations under the auspices of the International Olympic Committee have combined to recognise their role in minimising the potential effects of exertional heat stress. While exercise-associated collapse is a common phenomenon in endurance events this relatively benign condition must be distinguished from serious heat injury. The judicious supervision of events and astute observation of participating athletes will go some way towards preventing exertional, heat-related injuries.