Bacterial endocarditis is an infection in the lining of the heart. Germs normally live in your mouth and on your skin. They also live in your intestines and other parts of your body. If the germs get into the blood, they may infect the heart. This infection may over time involve the heart valves. People who have other heart problems can get this illness. You may also have this illness even if you do not have any other heart problem.