This study investigated the association between ambient pollution levels and cardiovascular function in 21 active Boston residents aged 53 to 87 years. Participants underwent repeated Holter ECG monitoring over 12 weeks, with 25 minutes of continuous monitoring each week. Pollution levels, including PM2.5 and ozone, were measured continuously. Heart rate variability (HRV) was assessed using time domain variables: SDNN and r-MSSD. Results showed that elevated PM2.5 levels were significantly associated with reduced HRV. During slow breathing, a 6.1 ms reduction in r-MSSD was linked to a 14.3 µg/m³ increase in PM2.5. A multiple pollution model showed a combined effect of PM2.5 and ozone reducing r-MSSD by 33%. The study suggests that particle and ozone exposure may decrease vagal tone, leading to reduced HRV. Reduced HRV is a predictor of increased cardiovascular mortality and morbidity. The study found that short-term increases in particle pollution were associated with increased cardiovascular mortality and morbidity. The findings indicate that ambient pollution may influence cardiovascular risk through autonomic dysfunction. The study also found that PM2.5 levels were most strongly associated with reduced HRV when measured over 4 hours before and including the Holter session. The study highlights the importance of monitoring pollution levels and their impact on cardiovascular health. The study's limitations include the use of time domain variables only and the small sample size. The study's implications suggest that short-term changes in HRV may have prognostic value for cardiovascular events. The study was supported by various grants and acknowledgments.This study investigated the association between ambient pollution levels and cardiovascular function in 21 active Boston residents aged 53 to 87 years. Participants underwent repeated Holter ECG monitoring over 12 weeks, with 25 minutes of continuous monitoring each week. Pollution levels, including PM2.5 and ozone, were measured continuously. Heart rate variability (HRV) was assessed using time domain variables: SDNN and r-MSSD. Results showed that elevated PM2.5 levels were significantly associated with reduced HRV. During slow breathing, a 6.1 ms reduction in r-MSSD was linked to a 14.3 µg/m³ increase in PM2.5. A multiple pollution model showed a combined effect of PM2.5 and ozone reducing r-MSSD by 33%. The study suggests that particle and ozone exposure may decrease vagal tone, leading to reduced HRV. Reduced HRV is a predictor of increased cardiovascular mortality and morbidity. The study found that short-term increases in particle pollution were associated with increased cardiovascular mortality and morbidity. The findings indicate that ambient pollution may influence cardiovascular risk through autonomic dysfunction. The study also found that PM2.5 levels were most strongly associated with reduced HRV when measured over 4 hours before and including the Holter session. The study highlights the importance of monitoring pollution levels and their impact on cardiovascular health. The study's limitations include the use of time domain variables only and the small sample size. The study's implications suggest that short-term changes in HRV may have prognostic value for cardiovascular events. The study was supported by various grants and acknowledgments.