Background: Fulminant myocarditis (FM) is a most fatal clinical manifestation of the viral myocarditis. However, cytokines have not been identified as a prognostic factor in coxsackieviral B (CVB) FM. To identify the prognostic factors in CVB FM, we compared the clinical courses and laboratory findings, including cytokines, at the time of admission between acute fulminant (FM, n=8) and non-fulminant (NFM, n=7) CVB myocarditis. Methods and Results: FM was defined as acute onset (within 2 weeks) of symptoms with cardiogenic shock, which needs intravenous inotropics and temporary mechanical assist device (MAD) including percutaneous cardiopulmonary support, ECMO and/or IABP. Myocardial biopsy was performed in nine patients. The main serotypes of CVB were CVB3 or CVB4 (5/7 in NFM, 7/8 in FM). Age, sex and initial echocardiographic fingings were not different between groups. MAD were applied to 7 FM patients within 12 hours after admission, and 6 FM patients were recovered within 2 weeks, one FM patient died despite heart transplantation. Among laboratory markers, initial CK-MB, leukocytosis, NT-proBNP levels were higher in FM, but insignificant. Furthermore, initial ejection fractions (EF), initial cTnI, ESR and CRP were not different. Among the initial cytokine levels, IL-6 (Mean짹SEM, 15.3짹4.27 vs 307.3짹138.9 pg/ml, P=0.009) and IL-10 (1.43짹1.3 vs 6.0짹2.3 pg/ml, P=0.03) were significantly higher in FM. In contrast, IL-12 (103.6짹28.1 vs 50.1짹8.7 pg/ml, P=0.05) was significantly higher in NFM. However, levels of TNF-a and TNF-a receptor type II were higher in FM, but insignificant. In FM, LVEFs were above 50% at the time of discharge, however, LVEFs remained below normal by 9 month after discharge. Pathologic findings such as inflammations, fibrosis were not different between groups, looked dependent on the timing of biopsy. Conclusion: Since the LV function in FM recovers completely within 1 month and has excellent long-term prognosis, the aggressive hemodynamic support should be applied as soon as possible. Among initial laboratory findings, levels of cytokines may be helpful to predict the course of acute CVB myocarditis, however, more data are needed to find the cut-off points for prediction.