Abstract: We reported a case of an elderly female patient with multi-organ involvement of the ear, eye, nose and heart, with elevated serum inflammatory markers and IgG4, and negative anti-neutrophil cytoplasmic antibodies. The patient was suspected to have granulomatosis with polyangiitis (GPA) combined with IgG4-related disease (IgG4-RD), because both GPA and IgG4-RD can lead to multi-organ involvement, with similar clinical manifestations and consistency in treatment. After treatment with high-dose glucocorticoid combined with cyclophosphamide, the clinical symptoms were relieved. The patient also had a high degree of atrioventricular block (AVB), which is rare in both GPA and IgG4-RD. In this paper we discuss the characteristics of the overlap syndrome, the diagnosis and treatment of this patient and the possible pathological mechanism of AVB, in order to provide reference for clinical treatment.