Cigarette butts and ash. Cigarette butts and ash in a heart-shaped ash tray. Tobacco contains the stimulant nicotine which is responsible for the addictive nature of cigarette smoking. Carbon monoxide in cigarette smoke passes from the lungs into the bloodstream. High levels of carbon monoxide cause hardening of the arteries, which increases the risk of coronary thrombosis and stroke. Smoking also increases blood pressure which can lead to heart failure. The tar and particles in tobacco smoke irritate the linings of the respiratory system leading to chronic bronchitis, emphysema and an increased risk of lung cancer.