This epidemiological study in Shanghai, China demonstrated that air pollution, low temperature and high temperature were important environmental triggers for OHCD, but not for IHCD. There may be some interactions between air pollution and temperature in triggering OHCDs. Overall, our results were generally robust to the smoothness of time trends, more aggressive control of temperature and the exclusion of days with extremely severe air pollution. To our knowledge, this is the first study in a highlypolluted developing country to evaluate the impact of air pollution on OHCD. This is also the first study to differentiate between