Abstract This was a study of 157 028 emergency department (ED)-diagnosed visits for chest pain ( International Classification of Diseases, Ninth Revision [ ICD-9]: 786) in 6 cities in Canada. The generalized linear mixed methods technique was applied to analyze the relations between daily counts of ED visits for chest pain on the levels of ambient air pollutants after adjusting for meteorological variables. The daily counts of visits were analyzed separately for the whole period (January-December), warm (April-September), and cold (October-March). The results are presented in the form of the excess risks associated with an increase in the mean values of the pollutant concentrations. The highest increase was obtained for nitrogen dioxide (NO 2) exposure in the warm period as follows: 5.9% (95% confidence interval, 3.3-5.8) for mean value equals to 20.1 ppb. The associations of ED visits for chest pain with air pollution are very similar to the associations of ED visits related to cardiac problems.