ETIOLOGY
Rheumatism is the cause of most instances of cardiac disease which date back to childhood or youth, while arteriosclerosis and chronic infection cause most cardiac diseases in the adult. In the former case it is the mitral valve which is the most frequently affected, while in the latter it is the aortic valve. Any cause which tends to induce arteriosclerosis may be a cause of chronic endocarditis, such as gout, syphilis, chronic nephritis, alcoholism, excessive use of tobacco, excessive muscular labor and hard athletic work. Lead is also another, now rather infrequent, cause. Severe infections may tend to make not only an arteriosclerosis occur early in life, but also a chronic endocarditis. Heart strain may also be a cause of chronic endocarditis, especially at the aortic valve. Forced marches of soldiers, competitive athletic feats, and occupations which call for repeated hard physical strain may all cause aortic valve disease. Tobacco, besides increasing the blood tension and thus perhaps injuring the aortic valve, may weaken the heart muscle and cause disturbance and irritation and perhaps inflammation of the mitral valve.
There is no age which is exempt from valvular disease, but the age determines the valve most liable to be affected. If endocarditis occurs in the fetus, it is the right side of the heart that is affected; in children and during adolescence it is most frequently the mitral valve that is involved; while in the adult or in old age it is the aortic valve that is most liable to become diseased. Statistics have shown that the valves of the left side of the heart are diseased nearly twenty times as frequently as those of the right side of the heart. They also show that the mitral valve is diseased more than one and one-half times as frequently as the aortic valve. Early in life probably the two sexes are equally affected with valvular disease, with perhaps a slight preponderance among females, because of their greater tendency to chorea. Females also show a greater frequency to mitral stenosis than do males. Aortic disease, on the other hand, from the very fact of their strenuous life and occupations, is nearly three times more frequent in men than in women.