The number of heart attacks in a U.S. city fell quickly when public smoking was banned, researchers have found.

In June 2002, Helena, Mont., banned smoking in workplaces, bars and restaurants. Opponents won a court order suspending the ban in December 2002.

To see if the smoking ban made a difference, researchers in California compared the city's June to December heart attack rates in each year from 1998 to 2003.

Smoke-free laws may be linked to rapid decrease in heart attacks

One hospital serves the region's 68,000 residents.

Medical Prof. Stanton Glantz of the University of California, San Francisco, and colleagues found hospital admissions for heart attack fell by 40 per cent in the city during the ban.

Twenty-four people were admitted with a heart attack during the six-month smoking ban, compared to an average of 40 before and after the ban.

There was no significant drop in admissions for people living outside Helena.

The geographical difference "suggests that smoke-free laws not only protect people from the long term dangers of secondhand smoke but also that they may be associated with a rapid decrease in heart attacks," the researchers wrote in Monday's online issue of the British Medical Journal.

Of heart attack patients in the study, 38 per cent were smokers, 29 per cent had quit and 33 per cent had never smoked.

Further studies are needed to confirm the small numbers suggesting that cutting exposure to secondhand smoke prevents heart attacks immediately, the researchers said.

But Glantz said the effect is consistent with what scientists know about the effects of secondhand smoke on heart disease, such as disturbing heart rhythms.

Cass Wheeler, CEO of the American Heart Association, said that the study should add to the momentum to ban smoking in public places.

A second study in the same issue found a 15 per cent higher risk of death among non-smokers who live with a smoker. The study was based on the 1981 and 1996 censuses in New Zealand among those aged 45 to 74.

Adults who never smoked and who lived with smokers had a higher risk of death after taking differences in age, ethnicity, marital status and socioeconomic position into account.