Four different heat wave definitions (as outlined by Hajat et al, 2006; D’lppoliti et al, 2010; Anderson and Bell, 2011; Nairn and Fawcett, 2013) were used to characterize heat wave mortality across the United States. The goal was to identify if certain definitions perform better or worse than others. Overall every definition performed poorly, resulting in high False-Alarm Ratios and low Heidke Skill Scores. However, the Nairn and Fawcett (2013) and Anderson and Bell (2011) definitions performed consistently better than the other definitions. Despite several limitations, the results of this study indicate that the heat wave definitions need refinement. Additionally, the Nairn and Fawcett (2013) definition could be one of the best definitions for assessing heat waves and heat-related mortality.