Heatwaves and cardiovascular mortality: Pathophysiological pathways, environmental co-determinants, and the role of autonomic monitoring

Background: Heatwaves are the deadliest extreme weather events, and their frequency and intensity are rising under anthropogenic climate change. In summer 2025 alone, an estimated 24,400 heat-related deaths occurred across 854 European cities, ∼68% attributable to human-induced warming. The cardiovascular system is disproportionately affected, yet the interplay between thermal stress, environmental pollutants, and individual autonomic vulnerability remains incompletely characterised. Objectives: To synthesise evidence on: (1) the epidemiological burden of heatwave-related cardiovascular mortality in Europe; (2) mechanistic pathways linking extreme heat and co-pollutants (PM2.5, ozone) to cardiac dysfunction; (3) autonomic dysregulation, via heart rate variability (HRV), as a marker of individual vulnerability; and (4) emerging wearable-based strategies for scalable risk monitoring. Methods: Narrative review of primary literature and epidemiological reports from PubMed, Web of Science, and grey-literature repositories (WHO, EEA, Copernicus C3S), January 2000-June 2026. Results: European heat-related excess deaths rose from ∼70,000 in 2003 to 61,672 in 2022, and an estimated 24,400 in just 10 weeks of 2025, despite two decades of heat-health action plans. Extreme heat acts synergistically with PM2.5 and ozone (interaction index SI 1.51 for cardiovascular mortality), potentiating sympathetic hyperactivation, myocardial ischaemia, arrhythmia, and thromboembolic risk. Reduced HRV (SDNN, RMSSD) amplifies risk in the elderly and in patients with heart failure, prior myocardial infarction, or ischaemic heart disease. Consumer-grade wearables now enable continuous, population-scale HRV surveillance. Conclusions: Heatwaves are cardiovascular emergencies requiring integrated epidemiological surveillance, mechanistic understanding, and precision monitoring. Population-wide wearable-based HRV monitoring, combined with personalised heat-health early warning systems, is a clinically actionable strategy to reduce excess cardiovascular mortality in a warming world.