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Context: Diesel exhaust (DE) has been shown to increase the risk of cardiac arrhythmias. Although biodiesel has been proposed as a safer alternative to diesel, it is still uncertain whether it actually poses less threat.Objective: We hypothesized that exposure to pure or 20% soy biodiesel exhaust (BDE) would cause less sensitivity to aconitine-induced arrhythmia than DE in rats.Methods: Spontaneously hypertensive (SH) rats implanted with radiotelemeters were exposed once or for 5d (4h) to either 50mg/m(3) (low), 150mg/m(3) (medium), or 500mg/m(3) (high) of DE (B0), 20% (B20) or 100% (B100) soy biodiesel exhaust. Arrhythmogenesis was assessed 24h later by continuous infusion of aconitine, an arrhythmogenic drug, while heart rate (HR), and electrocardiogram (ECG) were monitored.Results: Rats exposed once or for 5d to low, medium, or high B0 developed arrhythmia at significantly lower doses of aconitine than controls, whereas rats exposed to B20 were only consistently sensitive after 5d of the high concentration. B100 caused mild arrhythmia sensitivity at the low concentration, only after 5d of exposure at the medium concentration and after either a single or 5d at the high concentration.Discussion and conclusions: These data demonstrate that exposure to B20 causes less sensitivity to arrhythmia than B0 and B100. This diminished effect may be due to lower irritant components such as acrolein and nitrogen oxides. Thus, in terms of cardiac health, B20 may be a safer option than both of the pure forms.