Bacterial endocarditis is a rare, but often lethal, complication of cardiac valve replacement. The endocarditis is called "early" when it occurs within 2 months of the operation, and "late" when it develops after that period. Contamination of the prosthesis with bacteria may occur intra-operatively or post-operatively. The clinical diagnosis is often difficult in early endocarditis when another focus of infection is present and in late endocarditis in the absence of fever and positive blood cultures. Isolation of the pathogen from blood cultures is essential to the diagnosis and treatment. Therapeutic surgery now has wider indications than formerly. The incidence of this dangerous complication can only be reduced by well-planned and well executed prophylactic measures.