In an intravenous drug user presenting with endocarditis symptoms, which heart valve is most likely involved?

In the context of intravenous drug use, the tricuspid valve is the heart valve most commonly involved in cases of infective endocarditis. This occurs primarily due to the direct introduction of bacteria into the bloodstream from non-sterile injection practices. The tricuspid valve is situated anatomically in close proximity to the right atrium and receives venous blood returning from the body, which is where contaminated substances from intravenous use enter circulation.

Bacterial organisms, particularly Staphylococcus aureus, tend to colonize the tricuspid valve, leading to endocarditis that can manifest with symptoms such as fever, heart murmurs, and embolic phenomena. This differs from endocarditis due to other causes, where the left-sided valves, such as the aortic and mitral valves, might be more commonly affected, especially in cases related to prior valvular heart disease or conditions such as rheumatic fever.

While all valves can potentially be involved in endocarditis, the prominence of the tricuspid valve involvement in intravenous drug users makes it the most likely valve to be affected in this specific population.