During the 1985 air pollution episode, increases in heart rate determined by a resting electrocardiogram were present in a random sample. Even after adjusting for cardiovascular risk factors and meteorologic parameters, the increases in heart rate were apparent. Elevated heart rates were consistently observed in association with concentrations of SO, total suspended particulates, and CO. The effects of the episode seemed to be stronger in women than in men. However, no difference was observed when SO2, total