Within the first 20 minutes of quitting, your heart rate and blood pressure return to normal. After 12 hours, carbon monoxide in your blood decreases and your blood oxygen levels return to normal. Within 24 hours, your risk of heart attack begins to fall. At 48 hours, nerve endings begin to regrow and enhance your sense of taste and smell. In the first weeks of quitting, tiny hair-like structures in your lungs start to work again, sweeping irritants out of your lungs. Within a year, your risk of developing heart disease is half that of those who still smoke. After 10 years, your risk of dying of lung cancer drops to half that of a smoker.