These poisons circulating through the blood, sometimes set up a severe inflammation in the valves and the lining of the heart. Ulcers, or little wart-like growths, form on the valves; and these may either eat away and destroy entirely parts of the valves or, when they heal, leave scars which shorten and twist the valves out of shape, so that they can no longer close the openings. When this has happened, the heart is in the condition of a pump which will not hold water, because the leather valve in its bucket is broken or warped; and we say that the patient has _valvular_ or _organic_ heart disease. The disease which most frequently causes this serious defect is rheumatism, or rheumatic fever; but it may also occur after pneumonia, typhoid, blood poisoning, or even after a common cold, or an attack of the grip. This is one of several reasons why we should endeavor, in every way, to avoid and stop the spread of these infectious diseases; not only are they dangerous in themselves, but although only two of them, rheumatism and pneumonia, frequently attack the heart, all of them do so occasionally, and together they cause nearly nine-tenths of all cases of organic heart disease. Should you be unfortunate enough to catch one of these diseases, the best preventive against its attacking the heart, or causing serious damage, if it does, is a very simple one--rest in bed until the fever is all gone and your doctor says it is perfectly safe for you to get up; and avoid any severe muscular strain for several months afterward. This is a most important thing to remember _after all infections and fevers_, no matter how mild. Even where the heart valves have been seriously attacked, as in rheumatism, they will often recover almost completely if you keep at rest, and your heart is not overtaxed by the strain of heavy, muscular work, before it has entirely recovered. Ten days' "taking it easy" after a severe cold, or a bad sore throat, may save you a serious strain upon the heart, from which you might be months or even years in recovering. But even where serious damage has been done to the heart, so that one of its valves leaks badly, nature is not at the end of her resources. She simply sets to work to build up and strengthen and thicken the heart muscle until it is strong enough to overcome the defect and pump blood enough to keep the body properly supplied--just as, if you are working with a leaky pump, you will have to pump harder and faster in order to keep a good stream of water flowing. It is astonishing how completely she will make good the loss of even a considerable part of a valve.