smokefree.gov - What happens when you quit smoking? Within 20 minutes of quitting smoking, your body begins to heal.  See how it also improves your health in the years ahead. At 20 minutes, heart rate and blood pressure begin to drop.  At 12 hours, carbon monoxide levels in your blood return to normal. At 2 weeks - 3 months, lung function begins to improve and your heart attack risk begins to drop.  At 1-9 months, coughing and shortness of breath decrease.  At 1 year, the risk of coronary heart disease is cut in half. At 2-5 years, the risk of stroke is reduced to that of a non-smoker.  At 10 years, the risk of kidney and pancreatic cancer decreases.  At 15 years, the risk of coronary heart disease is the same as that of a non-smoker.