Decreased heart rate variability (HRV) is a marker of autonomic dysfunction and has been associated with future cardiac morbidity and mortality. HRV has been inconsistently associated with exposure to particulate matter (PM) air pollution. Fewer studies have examined whether air pollution exposure is a risk factor for cardiac arrhythmias. We aimed in this study to evaluate the relationships of heart rate variability and cardiac arrhythmias to PM exposures. Heart rate variability and arrhythmias were measured with ambulatory electrocardiographs using available raw data collected in a cohort panel study the National Institutes of Health, National Institute of Environmental Health Sciences (funded by NIH NIEHS R01 ES-012243). Electrocardiograph data (8,952 person-hours) were collected in 50 nonsmokers with coronary artery disease age 71 years and older living in four retirement communities in the Los Angeles air basin. Exposures included hourly markers of traffic-related PM and secondary organic aerosols, daily size-fractionated particle mass, and hourly outdoor criteria gases. Subjects were genotyped for the glutathione S-transferase M1 and T1 null (risk) alleles. Repeated measures regression analyses were adjusted for actigraph-derived physical activity and heart rate, temperature, day of week, season, and community location.