The American Heart Association says cigarette smoking is the most dangerous of the risk factors that can be controlled. The nicotine in cigarette smoke makes the heart work harder. The chemicals in cigarette smoke narrow the blood vessels in the arms and legs. The bad effects of smoking also occur in non-smokers who breathe smoke from those around them. Nicotine is not the only harmful chemical in cigarette smoke.
Carbon monoxide gets in the blood, too.
This decreases the amount of oxygen going to the heart and other parts of the body. Cigarette smoking also causes the clotting factors in the blood to become sticky and clump together. This clumping can harm the heart and blood vessels. No cigarette is safe. Many smokers who have switched to low tar and low nicotine cigarettes smoke more often or inhale more deeply.