Researchers from University College London and St George's, University of London have found a link between passive smoking and heart attack risk.
During the study, the team measured the levels of cotinine - a compound carried in the blood - at two time points 20 years apart - in non-smoking men who had a partner who smoked.
A blood cotinine level above 0.7ng/mL is associated with a 40pct increase in the risk of a heart attack. The researchers found that while in 1978-80, 73pct of men had a cotinine level above 0.7ng/mL, by 1998-2000 that proportion had fallen to 17pct.
However, despite the number of non-smoking men at risk having fallen, half of those who still had a high cotinine level (above 0.7 ng/ml) in 1998-2000 lived with a partner who smoked.
Non-smoking men who lived with a smoking partner had the average cotinine levels, almost twice the level associated with an increased risk of a heart attack.
"The decline in smoking together with restrictions on smoking in public places has created an environment where people are exposed to far less tobacco smoke," lead researcher Dr Barbara Jefferis, from University College London said.
"This has resulted in the dramatic fall in the number of non-smokers at an increased risk of a heart attack.
"However, we can clearly see that living with someone who smokes puts you at a heightened risk.
"If we are going to reduce people's exposure to tobacco smoke further then we will need to focus efforts on reducing smoking in the home," she added.
Professor Peter Weissberg, Medical Director at the BHF, said: "This research shows that a great deal of progress has been made in reducing exposure to potentially damaging environmental tobacco smoke over the past 20 years. Importantly, it also shows that people are now more at risk of exposure in their own homes than in public places.
"We cannot stop people smoking in their own home, but we would urge smokers to think of the risk they're exposing their non smoking friends and relatives to when they have a cigarette in the house," he added. (ANI)