The infection may begin at the time of a dental or medical procedure in someone who has a predisposing abnormality of their heart. It may also occur in someone who has had no previous problem with their heart, and who has not had any other procedure which is associated with a risk of endocarditis. Bacteria often find their way into our blood in the midst of our normal day. Activities such as chewing or having a bowel movement typically push some bacteria into the bloodstream. The body has set up elaborate and effective ways of dealing with these events the most important of which is a smooth and continuous surface throughout the heart and blood vessels.
Bacteria simply have no place to attach, and if they do, the body can kill the bacteria promptly.
If a large number of bacteria enters the bloodstream and a condition exists, such as some types of valve deformities, the bacteria can gain a foothold on an area where the lining is not perfect. These vegetations are often only lightly adherant to the valve, and may break off into the blood stream. These can act like clots, blocking off flow in the arteries where they travel. Furthermore, they can spread the infection to multiple places in the body. A person with this type of infection may initially have only vague and mild symptoms which are ignored by the patient or misdiagnosed by the healthcare practitioner.