Dr John Godleski and colleagues at Harvard School of Public Health conducted an exploratory study to test the effects of particulate matter exposure in dogs, which share many features of the human cardiovascular system. The investigators hypothesized that particulate matter might affect the animals' cardiac function, leading to arrhythmia, and might induce inflammatory responses and changes in pulmonary mechanical measurements. Twelve dogs were exposed to concentrated ambient particles (CAPs) that were 30 times their level in ambient Boston air. They evaluated the effects of CAPs on electrocardiographic (ECG) wave patterns and performed a sophisticated analysis of each dog's ECG to measure possible effects of particulate matter on other electrical properties of the heart: heart rate variability, which is influenced by the involuntary nervous system, and T wave alternans, a change in the heart beat pattern. The investigators also assessed whether changes in respiratory parameters or inflammatory responses were associated with CAPs exposure.