Metabolic syndrome increased susceptibility to the cardiovascular effects of exposure to PM2.5 in rodents, in a recent toxicological study. Metabolic syndrome was induced in a group or rats through a high-fructose diet, while control animals were maintained on a normal diet. Both groups were exposed to primary traffic PM2.5 and to photochemically-aged secondary organic aerosol, drawing air from a traffic tunnel. ECG and blood pressure were continuously monitored for each animal. Exposure to ambient levels of PM2.5 for animals with Metabolic Syndrome resulted in several lower measures of heart rate variability and cardiac function, and increased arrhythmia and breathing rates. Healthy rats on a normal diet displayed only decreased heart rate variability and only on the first day of exposure. The correlation between different measures of cardiovascular function and breathing suggests that the increased susceptibility in animals with metabolic syndrome may be the result of autonomic nervous system imbalances.