Heat-related deaths are modelled estimates (not observed counts) for the summer months (June–August) of 2000–2026 across 854 European cities (about 158 million adults aged 20+). The models relate daily average temperatures recorded in the ERA5 dataset to patterns of mortality for five different age groups, from 20–44 to 85 years and older. They also account for socioeconomic factors and the cities’ geographic location. The estimates shown use year-specific values for population and mortality rates. Counterfactual (without the climate crisis) death estimates use the same methods, but with human-caused warming subtracted from temperatures using climate models. The cities included in the dataset stem from the EU Urban Audit definition and in total cover 40 percent of the population across 30 European countries.