Since 2004, the Ministry of Solidarity and Health has been implementing the National Heat Wave Plan, which includes a weather monitoring and alert component and a public health surveillance component. During a heat wave, health surveillance is conducted by Santé publique France to quickly identify any unusual impacts, adjust management measures as needed, and contribute to feedback and the continuous improvement of the plan. This article describes the surveillance conducted during 17 heat waves that occurred between 2015 and 2017. An increase in mortality and in the use of emergency care for heat-related conditions was observed during all of these heat waves. The estimated excess mortality, compared to previous years, in the departments and during the periods in question, was 18% in 2015, 13% in 2016, and 5% in 2017. The heat waves that began in June 2015 and 2017 appear to be characterized by greater use of emergency care for heat-related illnesses among those under 75 years of age, with possible exposure in school and workplace settings. The observed impacts underscore the need to strengthen prevention efforts, particularly during yellow alerts, and more broadly among school and workplace populations. Finally, health surveillance has never led to changes in alert decisions made based on weather forecasts. It serves as a decision-making aid, but with significant limitations in data interpretation, and must be supplemented by more detailed analyses.