The rarity of endocarditis due to Klebsiella species limits its recognition. We report the case of a 63-year-old man, known to have a tight calcified aortic stenosis presenting with acute heart failure associated with high fever. Klebsiella oxytoca endocarditis was diagnosed based on three sets of positive blood cultures together with fluttering vegetation (11 mm × 14 mm) on the middle segment of the anterior leaflet of the mitral valve. After 6 weeks of intravenous ceftriaxone and gentamicin bi-therapy, the patient had completely recovered. This case illustrates how sporadic this condition is, for which early assessment and proper treatment are crucial to enhance the short outcomes.