Introduction: Although the impact of outdoor and indoor air pollution on cardiorespiratory morbidity and mortality has been described, the evidence linking this exposure to intermediate outcomes such as heart rate variability (HRV) is still controversial. The study aimed to estimate the magnitude and direction of the association among outdoor and indoor exposure to fine particulate matter (PM2.5) and HRV as a marker of cardiovascular autonomic function in adult population, with no history of symptomatic cardiovascular disease (CVD), resident in Bucaramanga Colombia. Methods: A cross-sectional study was conducted in 200 people older than 40 years. Measurements of indoor PM2.5 during 24-48 hours and outdoor PM2.5 during 6-days cycles were carried out for approximately 7 months. Parameters of HRV in the time and frequency domains were estimated from 5-minutes electrocardiographic signals. The association between exposure and outcomes was determined by using linear multiple regression analysis. Results: An association between exposure to outdoor and indoor PM2.5 and HRV, in both time and frequency domains was found. An increase of 1 μg/m3 in outdoor PM2.5 was associated with a statistically significant reduction in parameters such as the SDNN (β= -0.007; 95%CI: -0.014 -0.0002) and the HF (β= -0,002; 95%CI: -0,003 -0,0002). Similarly, associations between outdoor and indoor PM2.5 and the LF/HF and pNN50 were observed. Conclusions: The results support the existence of a negative impact of the exposure to PM2.5 on cardiovascular autonomic function, mainly parasympathetic, in general population free of CVD.