The overwhelming majority of assessments of future heat-related health impacts is based on projections of heat hazards superimposed on current socioeconomic conditions only, making the implicit assumption that drivers of heat stress risk other than climate change will remain the same. This leads to systematic bias in health adaptation. To address such drawback, the climate change research community has developed a new scenario framework, made of distinct sets of climate and socioeconomic scenarios. The few assessments of future heat-related health impacts that employed this new framework have focused on changes in exposure but have not accounted for future populations' adaptive capacity. We aim at providing the first European projections of heat-related health impacts that account for multiple changes in both socioeconomic and climatic conditions. By doing so, we also aim at addressing the challenge of accounting for projections of the wide array of determinants of adaptive capacity, exploring the full range of uncertainties through the use of multiple combinations of socioeconomic and climate scenarios, and determining the influence of varying levels of socioeconomic development on future heat-related health impacts, through changes in adaptive capacity and vulnerability. We used European Shared Socioeconomic Pathways to project a wide array of determinants of vulnerability, including adaptive capacity. We then employed the new scenario framework to assess future heat stress risk in Europe under multiple combinations of heat hazard (under the climate scenarios) and socioeconomic vulnerability (under the socioeconomic scenarios), at high spatial resolution (0.1°), up to 2050. We particularly focus on areas where people are concentrated, such as urban areas. Findings Heat-related health impacts will show a steady increase in three of the four most plausible futures. Spatial distribution of future risk is highly uneven, with Scandinavia and the Mediterranean region showing respectively low and high risk under all scenario combinations. Although mainly driven by changes in heat hazard, future heat-related health impacts are significantly influenced by varying levels of socioeconomic development, which largely affect future populations' vulnerability and adaptive capacity. In many regions, changes in future adaptive capacity can have a larger contribution to future heat stress risk than climate change. Socioeconomic development pathways should not be viewed solely as potential ways to reach a given level of radiative forcing, but also as significant and direct determinants of future climate risk, particularly when considering their impact on future populations' adaptive capacity. There is an undeniable necessity to consider the future state of vulnerability and adaptive capacity – and their uncertainties under varying levels of socioeconomic development – when assessing future heat-related health impacts and designing health adaptation strategies.