Endocarditis is infection and inflammation of the lining of a valve in the heart.

"Culture-negative endocarditis" is a type of endocarditis in which no causative organisms can be grown in a culture taken from the bloodstream. This sometimes occurs when blood cultures are drawn after treatment (antibiotics) has already been initiated, or if the culprit organism is a fastidious organism that is difficult to grow in readily available culture media.

Endocarditis is most likely to occur in people whose cardiac valves have certain predisposing factors for infection; for example, the valves may have been scarred in childhood by rheumatic fever, or are congenitally different from normal (bicuspid aortic valve, mitral valve prolapse). Persons with prosthetic valves (i.e., valves which have been surgically replaced) are also more prone to having bacteria land on them and grow prosthetic "vegetations". Other patients at increased risk for endocarditis are those with previous endocarditis or congenital heart diseases. Intravenous drug users are also at especially high risk of acquiring culture-negative endocarditis from contaminated syringes.

In patients with endocarditis there is usually an obvious source of infection, such as an infected intravascular catheter, a dental abscess, or an infected skin lesion but in many patients there is no history of infection.

An estimated 10,000 to 15,000 new cases of endocarditis are diagnosed yearly in the United States.