Isolated Pulmonary Valve Endocarditis Caused by Enterococcus faecalis—Facing the Unpredictable

<b>Background:</b> Infective endocarditis is a severe, life-threatening condition which affects the endocardial lining of the heart. Right-sided IE typically affects the tricuspid valve and, less commonly, the pulmonary valve, often in association with intravenous drug use and intracardiac devices. <i>Enterococcus faecalis</i>, a significant pathogen in healthcare settings, is frequently resistant to several antibiotics, complicating treatment. <b>Results:</b> We present the case of a 69-year-old man diagnosed with isolated pulmonary valve endocarditis, with no identifiable risk factors, good oral hygiene, and no recent dental procedures. In our case, the <i>E. faecalis</i> strain, initially susceptible to ampicillin, acquired resistance during high-dose ampicillin and gentamicin therapy, leading to cardiac surgery and prolonged antibiotic treatment. <b>Conclusions:</b> IPE is rare, emphasizing the need for heightened clinical awareness and thorough diagnostic evaluation, especially in patients with endocarditis symptoms and known risk factors. Although ampicillin resistance in <i>E. faecalis</i> is uncommon, its emergence during treatment presents a challenge, necessitating careful antibiotic stewardship to improve outcomes.