The authors report a rare case which is interesting from three points of view: tricuspid valve endocarditis in a child complicating a fistula between the right coronary artery and right ventricle with negative blood cultures but a positive serology for Coxiella burnetii. This mutilating tricuspid endocarditis was complicated by multiple pulmonary embolism of the right lung. After two months of antibiotic therapy the coronaro-cardiac fistula was closed and the tricuspid valve replaced with a mitral homograft. All cases of blood culture negative endocarditis require serological investigation to detect intracellular organisms which are difficult to diagnose and justify specific prolonged antibiotic therapy. Control serological tests are essential in the long-term because of the risk of chronic infection, especially in cases with prosthetic intracardiac material. Treatment, based mainly on tetracyclines, should be continued for at least two years.