Influence of extreme heat waves as an aggravating factor in the cause of death from cardiovascular diseases in Southeast Brazil.

Extreme heat waves (HW) have intensified with climate change and represent a growing threat to cardiovascular health. Brazil, particularly the Southeast region, concentrates densely populated metropolitan areas and is highly vulnerable to the health impacts of rising temperatures. This study aimed to estimate excess mortality from cardiovascular causes associated with HW events in Southeast Brazil between 2014 and 2023. We conducted a time-series analysis using aggregated mortality data from the Brazilian Informatics Health Department and meteorological data from Brazilian National Institute of Meteorology. HW intensity was classified via the Excess Heat Factor (EHF), and excess mortality was estimated using observed-to-expected ratios. Correlation analyses between temperature and mortality from hypertension and ischemic heart disease were performed. Eleven extreme HW were identified during the study period. Mortality from cardiovascular causes coincided with HW episodes, particularly among older adults and in the largest metropolitan areas. Results indicated excess deaths during specific events, with an unusual increase observed in the winter of 2022. The correlations between mean temperature and monthly mortality were weak or negative, reinforcing the need for robust indices such as the EHF to capture health impacts of extreme heat. HW events in Southeast Brazil were associated with higher cardiovascular mortality. The findings highlight extreme heat as a relevant public health risk and reinforce the need for early warning systems, targeted mitigation strategies, and policies for urban and occupational adaptation. These results demonstrate that HW significantly aggravates cardiovascular mortality in Brazil's most populous region.