A government study suggests that secondhand smoke is a very serious public health threat.

The study by the CDC says a smoking ban in a Colorado city led to a dramatic drop in heart attack hospitalizations within three years.

The study, the longest-running of its kind, showed the rate of hospitalized cases dropped 41 percent in the three years after the ban of workplace smoking in Pueblo, Colo., took effect. There was no such drop in two neighboring areas. Researchers believe it's a clear sign the ban was responsible.

One of the researchers says the study suggests that secondhand smoke may be a terrible and under-recognized cause of heart attack deaths in this country.

At least eight earlier studies have linked smoking bans to decreased heart attacks, but none ran as long as three years.