Objective To investigate reproducibility of outcomes for short-term associations between ambient air pollutants and acute myocardial infarction (AMI) hospitalisation in 2 urban populations.

Design Using a time-stratified design, we conducted independent case-crossover studies of AMI hospitalisation events over the period 1999–2010 in the geographically close and demographically similar cities of Calgary and Edmonton, Alberta, Canada. Patients with his/her first AMI hospitalisation event were linked with air pollution data from the National Ambient Pollution Surveillance database and meteorological data from the National Climatic Data Center database. Patients were further divided into subgroups to examine adjusted pollution effects. Effects of pollution levels with 0–3-day lag were modelled using conditional logistic regression and adjusted for daily average ambient temperature, dew point temperature and wind speed.

Setting Population-based studies in Calgary/Edmonton.

Participants 12 066/10 562 first-time AMI hospitalisations in Calgary/Edmonton.

Main outcome measures Association (adjusted OR) between daily ambient air pollution levels and hospitalisation for AMI.

Results Among 600 potential air pollution effect variables investigated for the Calgary (Edmonton) population, only 1.17% (0.67%) was statistically significant by using the traditional 5% criterion. None of the effect variables were reproduced in the 2 cities, despite their geographic closeness (within 300 km of each other), and demographic and air pollution similarities.

Conclusions Comparison of independent investigations of the effect of air pollution on risk of AMI hospitalisation in Calgary and Edmonton, Alberta, indicated that none of the air pollutants investigated—CO, NO, NO₂, O₃ and particulate matter (PM_2.5)—showed consistent positive associations with increased risk of AMI hospitalisation.