Infective endocarditis is an infection of the endocardial surface of the heart, most often a valve. It is uncommon, it is frequently missed early, and untreated it is close to uniformly fatal — which is why a patient with unexplained fever and a reason to have a susceptible heart deserves active suspicion rather than reassurance. What makes it distinctive is that it is an *endovascular* infection. The organism is not walled off in a tissue abscess; it is sitting on a surface washed by every litre of blood the heart moves. That single fact explains almost everything else about the disease: the persistent bacteraemia, the need for prolonged intravenous therapy, the fever that does not settle, and the sudden catastrophic complications when a fragment breaks free. This lesson is written for Canadian nurse-practitioner practice. It covers diagnostic reasoning under the modified Duke framework, culture strategy including culture-negative disease, imaging escalation, prosthetic valve and cardiac device infection, antimicrobial principles, surgical referral thresholds and current Canadian prophylaxis guidance. Laboratory values follow SI units. On the exam, writers often pair stable-sounding options with...