The risk for IE among IV drug abusers, 2 to 5 per cent per patient- year, is estimated to be several fold greater than that of patients with rheumatic heart disease or prosthetic valves. Endocarditis occurring in IV drug abusers has a unique propensity to infect right heart valves. In clinical series, distribution of valve involvement is tricuspid in 46 to 78 per cent, mitral in 32 to 24 per cent, and aortic in 8 to 19 per cent, (as many as 16 per cent of patients have infection at multiple sites). In IV drug abusers, the valves were normal before infection in 75 to 93 per cent of patients. In contrast to NVE among adults in general, S aureus causes more than 50 per cent of these infections overall and 60 to 70 per cent of those involving the tricuspid valve.