This article is a commentary on the study published in the journal *Epidemiology* 2003; 14(5):521-527. The study examines the relationship between air pollution—as defined by various indicators—and measures of heart rate variability in older adults. The results suggest that exposure to fine particulate matter and ozone leads to a decrease in the high-frequency HRV index among older adults living in Mexico City. This effect is particularly pronounced in individuals with hypertension. (Authors’ objectives and conclusion).