Here are some of the many benefits you will experience after quitting smoking: After 20 minutes: Blood pressure and heart rate lower. After 12 hours: The level of carbon monoxide in the blood returns to normal. After 24 hours: The risk of a heart attack decreases. After two to 12 weeks: Blood circulation improves. After one year: The risk of heart disease is half of that of a smoker. After five years: The risk of a stroke is now the same as that of a non-smoker. After 15 years: The risk of developing coronary heart disease is the same as a non-smoker.