IntroductionIncreased summer heat has a deleterious effect on people’s health and the healthcare system. Emergency Medical Services (EMS) are at the healthcare system frontline, responsive to the community and environmental conditions. The present study examined how EMS on-scene response is affected by community-level social vulnerability and heat.MethodsThe Centers for Disease Control and Prevention’s Social Vulnerability Index, heat and humidity data from the National Weather Service, and City of San Antonio EMS data were collected. Data were analyzed using negative binomial regression models with time-stratified case-crossover design to observe independent and interactive effects of heat and social vulnerability on EMS on-scene response over four constricted calendar years.ResultsResults indicated that community-based social vulnerability and heat, independently and interactively, are associated with increased EMS on-scene responses.ConclusionEven when examining normal summertime heat conditions, there is evidence of the relationships between geographic and environmental conditions and the healthcare system.