Being exposed to even a small amount of second-hand tobacco smoke may increase your chances of developing heart disease, according to Greek doctors.
They found people who are exposed to smoke just a few times a week could see their risk rise by 15% in five years.
Their study of more than 1,900 people also found that over 30 years that risk could have more than doubled.
Speaking at the European Society of Cardiology Congress in Vienna, they called for a ban on smoking at work.
An estimated three million people in the UK are exposed to second-hand smoke while at work.
Many more are believed to be inhaling smoke from someone else's cigarette at home.
Daily exposure
A study published earlier this year suggested passive smoking at work kills three people every day.
These latest findings are based on a study of 847 people with heart disease and 1,078 healthy volunteers by Dr Demosthenes Panagiotakos and colleagues at the University of Athens.
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A ban on smoking in workplaces might be an effective way to reduce exposure to second-hand smoke
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Dr Demosthenes Panagiotakos
All of these people were roughly the same age and lived in the same parts of Greece.
They were all asked if they were exposed to second-hand smoke for more than 30 minutes each day.
People with heart disease were much more likely to say they are regularly exposed to smoke from other people's cigarettes.
Some 86% of heart disease patients said they were exposed to second-hand smoke for more than 30 minutes each day. This compares to 56% of healthy volunteers.
Among non-smokers, people with heart disease were almost 50% more likely to be regularly exposed to second-hand smoke.
The researchers found that people who were exposed to second-hand smoke at home or at work were 15% more likely to develop heart disease.
That risk doubled if they were exposed for up to 30 years.
"Even a short exposure to second-hand smoke increases the risk of developing acute coronary syndromes," said Dr Panagiotakos.
"The only safe way to protect non-smokers from exposure to cigarette smoke is to eliminate this health hazard from public places and workplaces, as well as from the home.
"A ban on smoking in workplaces might be an effective way to reduce exposure to second-hand smoke."
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