Journal of the American Heart Association .
Cigarette smoking is a major risk factor for coronary heart disease.
This is the first study to demonstrate that the harmful effects of smoking extend beyond the heart's large arteries into the network of tiny blood vessels that supply blood to most of the heart muscle. These small vessels are not visible during angiography, a standard X-ray procedure that detects blood flow abnormalities. They found that the additional blood supply that should be available to the heart during stress was reduced by 21 percent in smokers compared with the non-smokers. Individuals in the study did not have symptoms of heart disease. The mechanisms by which smoking damages the coronary system is not fully understood but the researchers say their findings support the hypothesis that free radicals, or unstable oxygen molecules, in cigarette smoke may be responsible.