In an IV drug user with suspected infective endocarditis, which valve is most commonly infected?

• A. Aortic valve
• B. Mitral valve
• C. Pulmonic valve
• D. Tricuspid valve

Answer: (D)

In IV drug users, infective endocarditis most often involves the tricuspid valve because the infection is seeded via the venous circulation directly to the right side of the heart. When bacteria from the skin—most commonly Staphylococcus aureus—enter the bloodstream through injection, they travel to the right heart first, making the tricuspid valve the most likely site for vegetations to form. This pattern also explains why septic emboli often go to the lungs, leading to pulmonary symptoms. While left-sided valves (mitral and aortic) can be affected in endocarditis, they are less commonly involved specifically in IV drug users; the pulmonic valve is involved only rarely.