We present a case of a 57-year-old man with a giant-cell myocarditis that made its debut as a sustained ventricular polymorphic tachycardia interpreted in the context of old apical myocardium infarct, with a posterior evolution towards refractory heart failure, which finally needed urgent cardiac transplantation. We explain the characteristics of this unusual myocarditis, which has a poor prognosis, and also the results of the laboratory techniques that led to an equivocal diagnosis in this patient.