A sudden death likely due to mild anaphylactic reaction in a young man is described. Autoptic, histologic, immunohistochemical, and laboratory findings were strongly consistent with the diagnosis of a mild anaphylactic reaction. Genetic molecular analysis, performed on formalin-fixed, paraffin-embedded tissues, showed a mutation described as W822X in a family with electrocardiographic pattern typical of Brugada Syndrome. It results in a nonsense mutation generating a truncated form of the channel protein. The mutation is due to a point substitution of a guanine with an adenine residue (G2466A). Immunohistochemistry and laser scanning confocal microscopy on sections from heart formalin-fixed, paraffin-embedded tissues led us to confirm the cellular localization of the Na+ CP type Valpha (C-20) at the intercalated disks of ventricular myocytes and nearly 50% reduction in Na+ channels expression in ventricular myocytes when compared with control cases. We suggest that the anaphylactic reaction that occurred in the young man could serve as a trigger mechanism, responsible for his sudden death with a SCN5A mutation associated with the Brugada syndrome.