This article focuses on responses to ambient particles by the heart. Available data from human studies and animal studies are reviewed in an attempt to find a common understanding in the findings. The pathophysiologic mechanisms responsible for these health effects are likely to be complex, and it is highly probable that several different mechanisms work in concert. Current evidence suggests that inhaled particles exert their effects on the heart via the autonomic nervous system and via the coronary vasculature. Direct effects on the myocardium by inhaled ambient particles or their constituents require more research.