Abstract Fulminant myocarditis (MF) is an acute onset, rapidly progressive and potentially fatal inflammatory cardiomyopathy which could manifests with cardiogenic shock and incessant arrhythmias. There is often a need for aminic or mechanical support to the circulation in the acute phase, waiting to obtain a histological diagnosis as quickly as possible to establish a specific therapy. Mortality in the acute phases is high, with a worse prognosis than in other forms of presentation of myocarditis, even in the long term. We report the case of a 45–year–old Asian woman suffering from autoimmune hypothyroidism, who had been reporting atypical chest pain for about 3 days, associated with fever, asthenia, and vomiting. On admission, the patient was in cardiogenic shock; an echocardiogram revealed biventricular dysfunction. Pulmonary embolism and acute coronary syndrome were excluded. Blood tests showed a significant troponin rise, neutrophilic leukocytosis, and hypertransaminasemia. Anti heart antibodies (AHA) were negative. Amine support with dobutamine and norepinephrine was then started. The first EKG showed an advanced atrioventricular block with a ventricular escape with the need for emergency temporary PM placement. Right heart catheterization showed pressures in the pulmonary circulation at the upper limits with average resistance and reduced cardiac index. An endomyocardial biopsy (EMB) was performed, subsequently complicated by cardiac tamponade due to lead displacement, treated with urgent pericardiocentesis. At the end of the procedure, the appearance of incoming episodes of complete BAV was highlighted, for which ICD implantation was performed. The biopsy showed virus–negative diffuse acute lymphocytic myocarditis. Cortisone therapy was therefore started, with immediate benefit, until the aminic support was suspended. A follow–up echocardiogram showed a complete recovery of normal biventricular function. In MF, early diagnosis, and the possibility of establishing specific therapy are crucial to reduce mortality. EMB is the only method that allows you to make an etiological diagnosis and exclude a possible infectious genesis. The patient‘s prognosis, in fact, in addition to supportive therapy, depends on the possibility of establishing a targeted treatment as soon as possible, which in virus–negative autoimmune forms consists of an immunosuppressive therapy modulated on the patient‘s histological type and clinic.