Background Hot and cold air temperatures have been associated with fatal thrombotic cardiovascular disease, but evidence for non-fatal outcomes and drivers of susceptibility remains limited. Given the lasting cardiovascular effects of COVID-19 and its potential interaction with temperature exposure, we examined the impact of air temperature on thrombotic cardiovascular disease, as well as effect modification by COVID-19 and person-level characteristics. Methods We conducted case time series studies using whole-population electronic health records in England (Jan 2020-Dec 2022), linked with small-area daily mean air temperature. We estimated cumulative short-term effects of temperature on arterial thrombotic events (AEs), venous thrombotic events (VEs), acute myocardial infarction (AMI), and ischaemic stroke (IS), using conditional Poisson regression with distributed lag non-linear models, including interactions with COVID-19 status and person-level characteristics. Results Among 49,080,575 individuals, we identified 604,655 AEs, 215,090 VEs, 275,390 AMIs, and 231,485 ISs. Hot temperatures (99th percentile 23.1 degrees C vs median 10.8 degrees C) were associated with higher VE risk over 21 days (incidence rate ratio [IRR] 1.33, 95% CI 1.21-1.47), particularly among older adults, those with pre-existing conditions, and individuals of Black ethnic group. Cold temperatures (1st percentile -0.7 degrees C vs median) were associated with AMI over 14 days (IRR 1.13, 95% CI 1.05-1.21), especially among those aged 65 years and over. No associations were found for AEs or IS. Cold temperatures increased VE risk among individuals with COVID-19 in the prior 6 months (IRR 1.40, 95% CI 1.05-1.86), but not others. Conclusions Susceptibility to temperature-related thrombotic events varies across population groups and may change following recent infectious disease, such as COVID-19. Funding This work was supported by the British Heart Foundation Data Science Centre (grant SP/19/3/34678); awarded to Health Data Research UK. This work was also supported by core funding from the British Heart Foundation (RG/F/23/110103), NIHR Cambridge Biomedical Research Centre (NIHR203312) [*], BHF Chair Award (CH/12/2/29428), Cambridge BHF Centre of Research Excellence (RE/24/130011), and by Health Data Research UK, which is funded by the UK Medical Research Council, Engineering and Physical Sciences Research Council, Economic and Social Research Council, Department of Health and Social Care (England), Chief Scientist Office of the Scottish Government Health and Social Care Directorates, Health and Social Care Research and Development Division (Welsh Government), Public Health Agency (Northern Ireland), British Heart Foundation and the Wellcome Trust. *The views expressed are those of the authors and not necessarily those of the NIHR or the Department of Health and Social Care. Key words Ambient temperature, Thrombotic cardiovascular disease, Venous thromboembolism, Myocardial infarction, COVID-19.