The incidence of endocarditis is increased in patients with cardiac lesions causing turbulent flow. A 400-fold increase is observed in patients with prosthetic valves and a prior history of endocarditis. Other high risk lesions include rheumatic valvular disease, cyanotic congenital heart disease, and degenerative valve lesions. The smaller increased incidence in patients with mitral valve prolapse is important because of the high prevalence of mitral valve prolapse in the population. In addition, intravenous drug use and nosocomial bacteremia have emerged as important factors among patients with endocarditis.