This article is an analysis of the following study: Filleul L, Cassadou S, Medina S, Fabres P, Lefranc A, Eilstein D, Le Tertre A, Pascal L, Chardon B, Blanchard M, Declercq C, Jusot JF, Prouvost H, and Ledrans L. The relationship between temperature, ozone, and mortality in nine French cities during the 2003 heat wave. Environ Health Perspect. 2006; 114:1344-47.