Infective endocarditis (IE) is a microbial infection of the endothelial surface of the heart. The characteristic lesion, the vegetation, is a variably sized amorphous mass of platelets and fibrin in which abundant microorganisms and scant inflammatory cells are enmeshed. Heart valves are most commonly involved. However, infection may occur at the site of a septal defect or on chordae tendinae or mural endocardium. Both native valves and prosthetic valves can be involved.

The terms acute and subacute are often used to describe IE. Acute IE presents with marked toxicity and progresses to valvular destruction and metastatic infection and manifests within days to less than 2 weeks of onset of infection. In contrast, subacute IE evolves over weeks (> 2 weeks) to months with only modest toxicity and rarely causes metastatic infection. Acute IE is caused typically, although not exclusively, by staphylococcus aureus,and usually involves a normal heart valve whereas the subacute syndrome is more likely caused  by  viridans streptococci, enterococci, coagulase-negative staphylococci, or gram-negative coccobacilli.