Heat waves are the most emblematic example of how climate change affects health. In France, the National Heat Wave Plan (PNC) specifically targets those events that are likely to pose a risk to the entire exposed population, known as heat waves. This study describes changes in the population’s exposure to heat waves and the associated excess mortality in metropolitan departments since 1970. The periods of interest were identified by adapting the approach of the heat wave and health alert system. Excess mortality is estimated by comparison with previous years. A Poisson regression between mortality rates and heatwave intensity examined whether the response changed following the implementation of the PNC in 2004. 1,118 heatwaves were identified between 1970 and 2016. The most intense and longest heatwaves occurred in 1976, 1983, 2003, and 2015. The population exposed to at least one heat wave per year doubled between 1974–1983 and 2004–2013. Nearly 32,000 excess deaths were observed across all 921 heat waves identified between 1974 and 2013. During these events, a one-unit increase in intensity is associated with a relative risk (RR) of death of 1.17 [1.16; 1.18] before 2003 and an RR of 1.17 [1.10; 1.21] after 2003. This study demonstrates that changes in the frequency and geographical and temporal extent of heat waves are already being observed in France, resulting in increased population exposure. The lack of change in the relationship between heatwave intensity and mortality following the implementation of the PNC underscores that a very significant impact remains possible, particularly if intensities similar to or greater than those of 2003—which remains exceptional to this day—were to occur.