The National Fire Protection Association has released its annual report on firefighter fatalities in the United States, and a leading cause of on-duty deaths in the fire service remains cardiac issues despite those deaths hitting an all-time low in 2016. Last year's total of 69 on-duty deaths marked the fifth time in six years that the number was below 70, according to the NFPA's 2016 Report. The 26 deaths attributed to cardiac issues marked the fewest since the NFPA began this study in 1977,