Deaths tend to lag extreme heat and mortality data is generally not available for timely surveillance during heat waves. We analyzed daily weather, emergency medical system (EMS) calls flagged as heat-related, emergency department (ED) visits classified as heat-related, and natural cause deaths. We observed a 10% (95% CI: 4-16) mortality increase associated with one-day lagged heat-related EMS calls and a 5% mortality increase with one-day lagged ED visits (95% CI: 2-8). We conclude heat-related illness can be tracked during heat waves using EMS and ED data which are indicators of heat associated excess natural cause mortality.