Introduction – Heat waves lead to excess mortality and exacerbate the impact of certain comorbidities. However, there is a lack of long-term data on their effect on emergency department visits, aside from a few very specific heat-related conditions. The objective of this study is to examine the impact of heat on emergency department visits for three clinical syndromes that are not currently routinely monitored in France: acute kidney injury, cardiac decompensation, and myocardial ischemia. Methods – The study period covers the summers (June 1 to September 15) from 2015 to 2022 for the 12 departments of the Auvergne-Rhône-Alpes region. Health data were extracted from the SurSaUD® syndromic surveillance system (Health Surveillance of Emergency Department Visits and Deaths). A multivariate analysis of the average daily number of visits based on periods when heatwave thresholds were actually exceeded and periods of heightened vigilance was performed using negative binomial regression. Results – A total of 14,060 emergency department visits for acute kidney injury, 29,841 for cardiac decompensation, and 17,749 for myocardial ischemia occurred between 2015 and 2022 during the study periods in Auvergne-Rhône-Alpes. The risk of an emergency department visit for acute kidney injury increases by +47% (95% confidence interval, 95% CI: [39–56]) when temperatures exceed meteorological alert thresholds, regardless of sex, age, department, day, or month, or when the maximum temperature exceeds 24°C, with an increasing risk at very high temperatures. These effects were not observed for emergency department visits due to cardiac decompensation or myocardial ischemia. Conclusion – The risk of emergency department visits for acute kidney injury increases during heat waves and should prompt the implementation of specific measures to prevent this condition during the summer months.