Bloomington, Ind. -- After an Indiana county smoking ban was implemented, heart attack hospital admissions dropped 70 percent for non-smokers -- but not for smokers, a study found.

Lead author Dong-Chul Seo of the Indiana University Bloomington examined the effect of public smoking bans on heart attacks in non-smokers. He analyzed Delaware County, which had no smoking bans during the study period, and Monroe County, which prohibited smoking in restaurants, bars, retail spaces and workplaces.

The study, published in the Journal of Drug Education, exposure to secondhand smoke for just 30 minutes can rapidly increase a person's risk for heart attack, even if they have no risk factors such as high blood pressure, high cholesterol or previous heart surgery.

The smoke, which contains carbon monoxide, causes blood vessels to constrict and reduces the amount of oxygen that can be transported in the blood.

The researchers compared heart attack hospital admissions of the two Indiana counties, which have similar in demographics, before and after a county smoking ban was implemented in one.

"What concerns us is the fact that about half of all non-smoking Americans are regularly exposed to secondhand smoke, even though more than 500 municipalities nationwide have adopted some form of a smoking ban in public places," Seo said in a statement.

© 2007 United Press International.