A 63-year old male with prior bioprosthetic mitral valve replacement and coronary artery bypass graft surgery presented with dyspnea. C-reactive protein and white blood cells were elevated and serial blood cultures were negative. Transesophageal echocardiography showed a paravalvular leak and a thickened anterior leaflet of unclear either infective or degenerative origin. For differential diagnosis, cardiac 128-dual source computed tomography (CT) was performed. The CT image showed a thickened anterior leaflet and further revealed that the paravalvular leak was draining into a large wall thickened pseudoaneurysm with dense tissue adjacent suggestive for an abscess. Therefore, (18)fluorodeoxyglucose-positron emission tomography ((18)FDG-PET) was appended and fused with the CT images. There was no tracer-uptake surrounding the leak excluding an abscess. However, an increased (18)FDG-tracer uptake at the thickened anterior leaflet indicated active inflammation. During the subsequent cardiac surgery, vegetations were identified on the anterior cusp of the bioprosthetic valve. Intraoperative biopsy was taken and the cell culture was positive for Staphylococcus aureus. The pseudoaneurysm was repaired and the valve was replaced with a bioprosthesis. The patient was discharged uneventfully from hospital on day 12 and antibiotic treatment was continued for 4 weeks. In conclusion, our case indicates that (18)FDG-PET with cardiac CT image fusion may be a useful tool in patients with unclear focus of inflammation and possible bioprosthesis infection.