Phenanthrene (Phe) is a polyaromatic hydrocarbon found predominantly in fossil fuel and petroleum-based pollution. Previous research has shown that acute exposure to high concentrations of Phe is pro-arrhythmic in mice. To determine the arrhythmic potential of chronic low-level exposure to Phe 16 5-week-old mice and 16 20-month-old mice were fed 6ug/kg Phe daily for 10 weeks. Repeat ECG and echocardiography measurements were collected during the exposure period. All animal work was carried out in accordance with the UK animals (scientific procedures) act 1986. Following the 10-week exposure hearts were subjected to an ex-vivo arrhythmia challenge and tissue was collected for gas-chromatography mass-spectrometry and histological analysis. Preliminary analysis has revealed an increased susceptibility to arrhythmia in aged mice. 63% of aged mice exposed to Phe showed spontaneous arrhythmic activity ex vivo versus none of the control or young mice (n=8, t test- p<0.05). Phe exposure significantly increased arrhythmia induction following pacing, from 17% to 75% (n=8, t test- p<0.05). This difference was not present when hearts were treated with isoprenaline before pacing, suggesting bradycardia as an underlying mechanism for Phe induced arrhythmia.