Inhaling diesel exhaust fumes causes changes in the body that may make people more prone to heart attack or stroke.
European scientists found that blood clots are more likely to form in otherwise healthy people exposed to relatively high amounts of diesel engine exhaust for a short time.
This could cause a blocked vessel, heart attack or stroke.
The British and Swedish scientists said they did not know if the findings from their small study would be the same with exhaust from petrol-powered engines. Diesel engines spew many times more fine pollutant particles than petrol engines.
Based on the findings, they recommended that people with heart and artery disease exercise away from traffic congestion to avoid the effects of this pollution.
"The important long-term aims of research like this are to try to promote changes in public health initiatives," said Dr Andrew Lucking of the University of Edinburgh, one of the researchers in the study presented at a meeting of the American Heart Association in Orlando.
Dr Lucking said the researchers planned to test devices called particle traps that could be retrofitted on diesel engines to reduce diesel particles.
The study involved 20 healthy men aged 21 to 44. They breathed filtered air and also diluted diesel exhaust at a level approximating kerbside exposure on a busy road.
Compared to breathing filtered air, breathing air with the diesel exhaust increased clot formation roughly 20 to 25 per cent in the hours after exposure.
The researchers also found an increase in platelet activation in the blood.
Platelets play a main role in clotting.
Dr Daniel Jones, president of the American Heart Association, said: "The evidence for air pollution and cardiovascular disease being related is growing. It appears to be real. What we don't understand are some of the exact causal mechanisms."
In September, the same group reported that the hearts of heart attack survivors were far more likely to be starved of oxygen when exercising while breathing in diesel fumes.
- Reuters
