Infective endocarditis is a rare but clinically variable and difficult to diagnose disease. Delayed diagnosis of infective endocarditis can lead to total valve damage, which can require surgical treatment. We present a case report of a 36-year-old patient admitted to the hospital because of swelling and pain in the left shin and febrile fever. Two-dimensional transthoracic echocardiography was performed and infective endocarditis was suspec­ted. ¹⁸F-FDG PET-CT did not confirm the diagnosis of infective endocarditis and the patient was discharged as an outpatient with antibiotic therapy. The patient was readmitted with persistent inflammatory markers. Tran­sesophageal echocardiography showed a ruptured mitral valve with severe regurgitation. When the inflammatory parameters were reduced by antibiotic therapy, the patient underwent mechanical mitral valve replacement surgery. The patient had an uncomplicated postoperative period.