We report the case of a 11-year-old girl with fulminant myocarditis and cardiogenic shock who received cardiopulmonary resuscitation and extracorporeal membrane oxygenation support. During the induction of hypothermia, her rhythm degenerated into idioventricular rhythm with extremely prolonged QRS duration. The hypothermia-induced bradycardia caused a drop of mixed venous oxygenation saturation and which was resolved by re-warming to normothermia. This finding suggested that hypothermia may compromise cardiac performance and physicians should be cautious about its application in patients with fulminant myocarditis.