This article assesses the effect of extreme heat on mortality in France for the period 1980-2019, using a new monthly database of French municipalities. By leveraging year-to-year random variations in temperature, I show that extreme heat significantly increases the mortality rate, especially for people aged over 80. However, the impact of heat decreased after the major heatwave of 2003 due to the public and private measures that followed. Days over 30°C are 7 times less deadly for people aged over 80 for the period 2004-2019, compared with the period 1980-2003. The study also highlights the greater vulnerability of people living in densely populated cities, where xtreme heat is 2.5 times more deadly for the elderly. Mediterranean municipalities, on the other hand, are more resilient than the rest of France, due to the population’s acclimatisation to heat and a higher air-conditioning equipment rate. In fact, days above 30°C has 5.6 times less impact on the overall mortality rate in Mediterranean municipalities compared to the rest of France. Finally, I estimate the future trend of heat-related deaths due to climate change. In the medium term (2041-2070), global warming will multiply by 5 the number of deaths of people aged over 75 due to maximum temperatures above 35°C, if current adaptation methods are not improved and if greenhouse gas concentrations continue to rise at the current rate.