According to Cancer.org, after only 8 hours of your last cigarette, the oxygen levels in your blood increase. After 12 hours, your carbon monoxide blood levels drop to normal. After 2 days of not smoking, you’ll have heightened senses of smell and taste. 3 days later, your bronchial tubes relax and breathing may feel less labored than before. During the first 9 months smoke free, your shortness of breath will improve, and the tiny cilia hairs in your lungs will regain function, allowing your body to clean your lungs. After 1 full year, your risk of heart disease is about half compared with a smoker. After 15 years of being smoke-free, your risk of a heart attack falls to the same as someone who has never smoked.