Since 2004, France has implemented the National Heat Wave Plan to prevent the health consequences of heat waves. Under this plan, the French Institute for Public Health Surveillance is responsible for issuing alerts and monitoring the health impact of heat waves. Alert proposals are based on weather forecasts provided by Météo-France, in accordance with the rules defined by the heat wave and health alert system. A description of the health situation in the departments affected by the alert can be useful for decision-making, particularly when determining the level of measures to be taken or declaring the end of an alert. Drawing on experience gained since 2004 and a review of the literature, the list of health indicators to monitor during heat waves has been redefined, focusing on mortality, emergency room visits, and reasons for contacting SOS Médecins. These indicators are monitored during the summer in each metropolitan department. Two statistical methods for detecting unusual events—a control chart method and the historical limits method—are proposed to aid in the interpretation of these indicators. We also propose a method for obtaining a rapid estimate of the impact on mortality following a heat wave. This indicator will make it possible to compare the impact of heat waves over time and to derive hypotheses to guide more in-depth studies. This work will help improve the effectiveness of the heat wave and health alert system, which must be responsive and robust, in a context of growing vulnerability to heat waves. (R.A.)