France has suffered last summer an unprecedented heat wave that led to an exceptional short-term surge of mortality. Cumulative deaths between August 1st to 14th are estimated at 14,800. Epidemiological studies carried out by the Institute de Veille Sanitaire will show the circumstances and risk factors leading to heat-related pathologies. A literature review already shows the principles of prevention, the circumstances of occurrences during similar past heat waves, the risk factors and the principles of treatment. Prolonged exposure to heat can be the initial cause of death, mainly in the elderly. The subject thus dies of an overload of his natural defenses, unable to preserve his thermal homeostasis. This is then a heat shock that reaches the central nervous system. Heat shocks could kill every second patient and leads to severe neurological sequel. During a heat wave, high temperatures can also trigger or worsen other illnesses or be responsible for other so called heat-related syndromes. It is crucially important to identify subjects at risk, situations of risk, and preventive measures, knowing that heat shock leads 25% of patients to develop multi-organ failure, even when appropriately treated.