['Heart rate alterations associated with exposure to particulate matter (PM) and gaseous pollutants have been observed in epidemiological studies and animal experiments. Nevertheless, the time-lag of these associations is still unclear.', 'Determine the association at different time-lags between the complex mixture of ambient concentrations of PM, carbon monoxide (CO), and nitrogen dioxide (NO(2)), and markers of cardiac function in a model of aged mice.', "AKR/J inbred mice were exposed to ambient air, 6 h daily for 40 weekdays. During this period, the animals' electrocardiogram (ECG), deep body temperature (Tdb), and body weight (BW) were registered, and concentrations of PM, CO, NO(2), as well as air temperature and relative humidity (RH) were measured. Data analysis included random effects models with lagged covariate methods.", 'CO was significantly associated with declines in heart rate (HR) and heart rate variability (HRV), PM was significantly associated with declines in HRV and BW, and NO(2) was significantly associated with declines in HR. Some significant associations occurred in the same day (PM and HRV, PM and BW, CO and HR), whereas others were delayed by 1 to 3 days (CO and HR, CO and HRV, NO(2) and HR, PM and HRV).'] Does ambient air pollution alter heart rate regulation in aged mice?