Carbon monoxide, when inhaled during smoking is absorbed in our blood. It then moves into the red blood cells. Then it combines rapidly with the hemoglobin, leaving less hemoglobin available to carry oxygen. Carbon monoxide increases the rate at which fatty substances are deposited on the inner walls of arteries, causing their lumen to become narrow. This way the risk of atherosclerosis is increased. It damages the lining of blood vessels which increases the tendency of the blood to clot, which results in blocked blood vessels.