Smoking

Smoking a cigarette causes your adrenal glands to secrete a hormone that temporarily increases your blood pressure and makes your heart work harder. Smoking also decreases the amount of oxygen available to your heart.

Why is less oxygen available?

Tobacco smoke contains carbon monoxide gas. When this is inhaled, it binds to the hemoglobin in the blood, taking the place of valuable oxygen.
                

What other dangers does carbon monoxide pose?

Research indicates that carbon monoxide may have a direct degenerative effect on the heart muscle itself and on the blood vessels.

Smokers  have more atherosclerosis--hardening of the arteries--than nonsmokers do.

Smoking has the following effects on the heart:

    Damages the lining of the arteries.
    Raises total cholesterol.
    Lowers HDL (the "good," protective cholesterol)

    Increases the stickiness of the platelets, making a clot
        in the narrowed arteries more likely.
    Makes the heart beat faster, which requires more oxygen,
       yet carbon monoxide in smoke makes less oxygen available.
    Raises blood pressure temporarily.

    May constrict coronary arteries, which makes them less
        able to supply oxygen to the heart when physical exertion
        demands, hence, people wind up "out of breath".