15 years has been established as the safety point for former smokers as a study has shown the risk of heart failure and death ceases to exist after 15 years of non-smoking.

However,  those who were heavy smokers, meaning at least a pack a day for 32 years or more, still have an elevated risk, even after 15 years.

Senior author Dr. Ali Ahmed of the Center for Health and Aging, Washington DC VA Medical Center and team used the ongoing Cardiovascular Health Study of adults over age 65, which included 2556 people who had never smoked, 629 current smokers and 1297 former smokers who had quit at least 15 years earlier.

Of those who had quit, 312 had been heavy smokers, with 32 “pack-years” or more of smoking.

After 13 years of follow-up, about 21% of never smokers and 21% of former smokers experienced heart failure.

But among former smokers with at least 32 pack-years, almost 30% suffered heart failure.

When the researchers accounted for other factors like age, sex, race, education, other health conditions and medications, current smokers were about 50% more likely to have heart failure than never smokers or former smokers.

The research finding was reported in Circulation: Heart Failure.

Moreso, over the same time period, current smokers were twice as likely to die from any cause, compared to never-smokers, and former heavy smokers were about 26% more likely than never-smokers to die.

According to Dr. Gerasimos Siasos of Brigham and Women's Hospital in Boston, Massachusetts, who was not part of the study,

Former heavy smokers may not achieve the health profile of never smokers, but the cardiovascular risk for them is definitely lower compared to current smokers

Another health practitioner also noted that the body heals itself and "within 12 hours or few days after the smoking, the level of carbon monoxide in blood will decline and the circulatory system will start repairing the damage.”