This study was undertaken to determine whether there was an association between air pollutant levels and emergency room (ER) visits for cardiac arrhythmia in Taipei, Taiwan. ER visits for cardiac arrhythmia and ambient air pollution data for Taipei were obtained for the period 20002006. The relative risk of ER visits was estimated using a case-crossover approach, controlling for weather variables, day of the week, seasonality, and long-term time trends. In the single-pollutant model, on warm days (³23¡C), statistically significant positive associations were found for all pollutants except SO2. On cool days (<23¡C), all pollutants were also significantly associated with the number of ER visits for cardiac arrhythmia, except SO2. For the two-pollutant model, results for O3 and NO2 remained statistically significant on both warm and cool days. This study provides evidence that higher levels of ambient air pollutants increase the risk of ER visits for cardiac arrhythmia.