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The effects on heart rate variability (HRV) and arterial stiffness from exposure to ambient particulate matter and ozone have not been studied simultaneously. The aim of this study was to analyze these effects with refined exposure estimates from personal measurements of ozone and size-resolved particulate matter mass concentrations. The authors recruited 17 mail carriers in a panel study in Taipei County, Taiwan, during February-March, 2007, and each subject was followed for 5-6 days. Personal ozone and size-fractionated particulate matter exposures were monitored during working hours while carriers delivered mail outdoors. Cardiovascular effects were evaluated with heart rate variability (HRV) indices and an arterial stiffness index, the cardio-ankle vascular index (CAVI). The authors used linear mixed models to examine the association between personal exposure data and the HRV index and CAVI. They found that an interquartile range increase in personal exposure to ozone and particulate matter of between 1.0 and 2.5 microm was associated with a 4.8% and 2.5% increase in CAVI, respectively, in the single-pollutant models. In contrast, the personal exposure data showed no significant effects on HRV. In 2-pollutant models, personal ozone exposure remained significantly associated with the CAVI measurements. The study results indicate that vascular function may be more sensitive to air pollutants than the autonomic balance.