Abstract Background Necrotizing coronary vasculitis (NCV) is a rare entity usually associated to myocarditis (M), which incidence, cause and responsiveness to therapy is unreported. Purpose We set out a retrospective study to report our experience in the diagnosis and management of myocarditis-associated necrotizing coronary vasculitis (M-NCV) and patients' outcome. Methods Among 5180 patients undergoing endomyocardial biopsy in our institution, 1916 received a histological diagnosis of myocarditis with associated NCV in 30 (12F, 18M, mean age 47.7 years±15). NVC endomyocardial samples were retrospectively evaluated with, immunohistochemistry for Toll like Receptor 4 (TLR4) and real-time PCR for viral genomes. Serum samples were processed for anti-heart autoantibodies and inflammatory cytokine profile (ELLA assay).Identification of an immunologic pathway (virus-, TLR4+, anti-heart abs +) was followed by immunosuppression including steroids, azathioprine, cyclophosphamide, high dose immunoglobulins and anakinra. M-NCV patients were followed for 6-months with resting ECG, Holter monitoring, 2D-echo and in 45% of cases with cardiac magnetic resonance. Increase of ≥10% in left ventricular EF was classified as response to therapy. M-NCV patients were compared to a control group of 60 consecutive patients with virus + and − lymphocithic myocarditis and a control group of 30 patients with mitral stenosis and normal LV size and function, undergoing surgical repair. Results 26 M-NCV patients presented with heart failure or cardiogenic shock; 3 with electrical instability; 1 with infarct-like symptoms. Cause of M-NCV included infectious agents (PVB19, HHV2, EBV and co-infection of Toxoplasma gondii and PVB19) in 4 patients; chest trauma in 1; drug-hypersensitivity in 2; hypereosinophilic syndrome in 1; primary autoimmune disease in 7; giant cells in 3; while it was idiopathic in the remaining cases. CMR imaging did not detect any qualitative difference between M-NVC and M patients. Anti-heart autoantibodies were positive in immune-mediated M-NCV and virus- M; in M-NCV patients in which anti-heart autoantibodies were positive, we found a cross-reaction with vessel walls. Myocardial expression of TLR4 was high in the immune-mediated forms and negative in the viral. Interleukins 1-beta was more elevated (p<0.001) in patients with M-NCV in comparison with virus-M patients. M-NCV patients presented a more severe clinical profile with 24% in-hospital mortality compared with 1.5% of the M group. Immunosuppression resulted in an improvement of cardiac function in 86% of M-NCV and 88% of virus-M cohort. Conclusion NCV can be histologically detected in up to 1.5% of a large population with myocarditis. Major causes include viral, autoreactive and autoimmune processes. Intra-hospital mortality is high (24%). Presence of an immunologic pathway is associated with a beneficial response to immunosuppression. Funding Acknowledgement Type of funding source: Public grant(s) – EU funding. Main funding source(s): European Project ERA-CVD