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.