Cardiac valvular involvement in antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis is very rare. We report the case of a patient seen in 2019, followed for ANCA-associated vasculitis for 15 years, who had a first relapse with cardiac valvular involvement in 2012, and who underwent a second histologically proven vasculitis relapse involving mitral periprosthetic endocardium. PET/CT imaging showed an intense and focal FDG activity of paramitral bioprosthesis leak site. Mitral bioprosthesis was replaced, and the patient improved with steroids and rituximab. Through this exceptional case, we suggest that FDG PET/CT could be of interest in the follow-up of ANCA-associated vasculitis with cardiac valvular involvement.