Pueblo, Colorado, passed a municipal law making workplaces and public places smoke-free in 2003 and U.S. Centers for Disease Control and Prevention officials tracked hospitalizations for heart attacks afterward.
They found there were 399 hospital admissions for heart attacks in Pueblo in the 18 months before the ban and 237 heart attack hospitalizations in the next year and a half -- a decline of 41 percent.
The effect lasted three years, the team reported in the CDC's weekly report on death and disease.
"We know that exposure to second-hand smoke has immediate harmful effects on people's cardiovascular systems, and that prolonged exposure to it can cause heart disease in nonsmoking adults," said Janet Collins, director of CDC's National Center for Chronic Disease Prevention and Health Promotion.
"This study adds to existing evidence that smoke-free policies can dramatically reduce illness and death from heart disease."
Long-term exposure to secondhand smoke can raise heart disease rates in adult nonsmokers by 25 percent to 30 percent, the CDC says.
Secondhand smoke kills an estimated 46,000 Americans every year from heart disease alone. Smoking also causes a variety of cancers, as well as stroke and emphysema or chronic obstructive pulmonary disease.