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Cat scratch disease (CSD), caused by Bartonella henselae, is an uncommon cause of fever of unknown origin (FUO) and rarely presents with visceral organ involvement. This case report describes a middle-aged woman with 3 months of night sweats and 1 month of fevers. Initial workup showed elevated inflammatory markers, multiple splenic lesions and a pelvic fluid collection. A detailed history noted that she recently adopted a stray kitten, prompting Bartonella serological testing. Given the atypical presentation, a broad infectious evaluation was also pursued, including testing for mycobacterial, fungal and other bacterial pathogens. When B. henselae IgG titre returned strongly positive and transoesophageal echocardiogram (TEE) showed a tricuspid valve vegetation, the diagnosis of culture-negative endocarditis was established. Treatment with doxycycline and rifampin led to rapid symptom resolution.This case highlights the potential for CSD to present as right-sided endocarditis. Clinicians should consider B. henselae infection in patients with FUO and cat exposure, even without classic regional lymphadenopathy. Due to its fastidious nature, B. henselae often evades culture, underscoring the role of serological or molecular testing in diagnosis. This report emphasises the diagnostic challenges of culture-negative endocarditis and the critical importance of detailed exposure history in guiding targeted diagnostic testing and stepwise serological evaluation in atypical disease patterns.