A continuous drop in heart attack fatalities in Massachusetts can be traced to the state’s 2004 ban of smoking in public places, according to a report released Thursday by the Harvard School of Public Health and the Massachusetts Department of Public Health.

The Massachusetts Smoke-free Workplace Law, which went into effect in July 2004, made smoking illegal in most indoor public places, including offices, bars, and restaurants.

Researchers evaluated death certificates from 1999 to 2006 and found that the yearly decrease in heart attack deaths has averaged to 577 since the ban was implemented. The number of deaths from heart attack per year decreased by 16 percent overall from 2004 to 2006.

This change comes hand-in-hand with a 15 to 20 percent decrease in hospitalization for heart attacks statewide.

“If you look at the biggest decline in heart disease deaths in Massachusetts overall, you see a kink in 2004. It’s not a general [phenomenon]—something happened in 2004,” said Joel Schwartz, an HSPH and Harvard Medical School professor who was involved in research for the study.

Schwartz also said he was not surprised to see changes in public health occur within two years of the implementation of the ban. “Cardiovascular death rates have been falling for a whole host of reasons. If you implement a policy and you implement it relatively suddenly, then the change would happen fast,” he said.

Researchers categorized cities and towns into three groups: those that had strict smoking laws prior to 2004, those with weaker laws at that time, and those with no smoking restrictions at all. They found that cities that had already had stricter laws, such as Boston and Cambridge, experienced changes in cardiovascular fatalities earlier, corresponding to when their regulations were modified.

Cities with weak or no laws, such as Worcester, saw dramatic shifts in public health after the implementation of the statewide ban. By the end of 2006, there was virtually no difference in rates of heart attack fatality throughout the state.

There has been an overall decrease of about 35 to 40 percent in cardiovascular fatalities in Massachusetts since 1999. Taking into account factors such as flu outbreaks, air pollution, and seasonal differentiation in health, scientists found that a reduction in secondhand smoke was the single greatest factor in the drop in deaths from heart disease.

A spokeswoman from the Massachusetts Department of Public Health said that the trends seen so far are expected to continue.

Thomas Land of the Department of Public Health, the lead researcher on the study, said he hoped the evidence motivates other states to pass laws of this ilk.

“Some states have passed smoking bans but haven’t put any teeth into them,” Land said.