Pre-print, Working paper: This paper studies the determinants of the regional disparities in the mortality of patients treated in a hospital for a heart attack in France. These determinants can be some differences in patient characteristics, treatments, hospital charateristics, and local healthcare market structure. We assess their importance with an exhaustive administrative dataset over the 1998-2003 period using a stratified duration model. The raw disparities in the propensity to die within 15 days between the extreme regions reaches 80%. It decreases to 47% after controlling for the patient characteristics and their treatments. In fact, a variance analysis shows that innovative treatments play an important role. Remaining regional disparities are significantly related to the local healthcare market structure. The more patients are locally concentrated in a few large hospitals rather than many small ones, the lower the mortality.