The bacteria causing infective endocarditis have not changed significantly despite the diversity of potential portals of entry. Streptococci (viridans) cause 35 to 45% of cases of endocarditis. Group D streptococci of gastrointestinal origin cause about 20% of cases of endocarditis: Streptococcus bovis is the most commonly isolated species followed by the enterococcus. The beta-haemolytic streptococci of Groups A, B, C and G are rarely isolated. Seventeen to thirty per cent of endocarditis is caused by staphylococci, above all Staphylococcus aureus. These infections are mainly observed in patients with prosthetic valves or intravenous catheters and in intravenous drug addicts. With respect to gram-negative bacilli, enterobacteria are rarely responsible for endocarditis and those of the HACEK group (Haemophilus, Actinobacillus, Cardiobacterium, etc.) were isolated in 3% of cases. Q fever and Chlamydia endocarditis are rare, as are fungal infections usually due to Candida. Endocarditis with negative blood cultures is still observed in about 10% of cases.