In the summer of 2022, our team of climatologists and researchers piloted the first heat warning system that ranks heat events based upon human health outcomes. This system uses local all-cause mortality data in addition to meteorological factors including air mass identification and the Excess Heat Factor (EHF) to identify heat events that are likely to endanger human health in the region and applies three categories representing increasing severity. In this study, we explain our rationale for ranking heat waves and using health metrics in a heat warning system and evaluate this system by comparing its calls in Seville, Spain between 1995 and 2022 with those of the Spanish national meteorology agency (AEMET), as well as against all-cause mortality data over the same time period. We find that our system captures more dangerous heat events than the meteorology-only criteria of AEMET and that the majority of identified heat events occurred during periods of elevated mortality. Over the last two years, stakeholders in Seville used this heat wave ranking system to better prepare for and respond to dangerous heat events. The system will continue to be deployed in Seville during upcoming summers, and it will expand to other regions as well.