Exposure to PM2.5 increases the total daily cardiovascular mortality by an estimated 3‐4% for every 25 μg/m3 increase in PM2.5. Impaired cardiac autonomic function, indexed by reduced heart rate variability (HRV), is one underlying cause. We previously showed that 3 d (6 hr/d) of PM2.5 exposure in the form of iron‐soot reduced HRV in mice. Here we test the hypothesis that exposure to airborne PM impairs vagal regulation of HRV by decreasing the excitability of the cardiac vagal neurons in the nucleus ambiguus (NA) in C57BL/6 mice. We measured 24 hr HRV in time domains from ECG telemetry recordings obtained in conscious freely moving mice. In parallel studies we determined the intrinsic properties of anatomically identified NA cardiac vagal neurons, retrogradely labeled with a fluorescent dye (DiI) applied to the SA node. PM2.5 exposure in the form of soot decreased the short term HRV (rMSSD). With the addition of iron, all HRV parameters were significantly reduced. The reduced HRV is more prominent during the dark cycle of the day. Blocking the vagal influence with Methylatropine significantly reduced all HRV parameters suggesting that HRV is under vagal regulation in mice. PM2.5 exposure also decreased the spiking responses of the identified cardiac vagal neurons to depolarizing current injections (P<0.05). The data suggest PM‐induced neuroplasticity of cardiac vagal neurons maybe one mechanism contributing to the cardiovascular consequences associated with PM exposure seen in humans. (Support: Support: 1R01ES012957‐01).