Climate change is increasing the frequency and severity of extreme heat events. These events affect cities in increasingly abrupt and catastrophic ways; yet, many of the deaths caused by exposure to heat have gone unnoticed or are inaccurately identified, resulting in a lack of urgency in addressing this issue. We aim to address this under-identification of deaths from heat waves in order to better assess heat risk. We investigated death records in New York City from 2010 to 2012 to identify characteristics that vary between deaths officially categorized as caused by heat wave exposure (oHDs) and those possibly caused by heat (pHDs). We found that oHDs were more often black and of a younger age than would typically be expected. We also found that there was a lack of evidence to substantiate that an oHD had occurred, using the NYC official criteria. We conclude that deaths from heat waves are not being accurately recorded, leading to a mis-estimation. Training regarding the collection and interpretation of evidence may improve preparedness for heat events.