In intravenous drug user-associated endocarditis, which heart valve is most frequently affected?

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

Answer: (A)

In intravenous drug user endocarditis, the infection most often involves the right side of the heart because bacteria are introduced directly into the venous circulation and seed the valves that venous blood returns to first. The tricuspid valve is the valve most frequently affected, leading to tricuspid regurgitation and commonly causing septic emboli to the lungs, which explains symptoms like fever and pulmonary findings. Left-sided valves such as the aortic and mitral are less commonly involved in this setting unless there are preexisting valve abnormalities or sustained bacteremia, and involvement of the pulmonic valve is rare. So the tricuspid valve aligns with the typical pattern seen in IV drug use.