Flavin adenine dinucleotide (2 mg/kg, i.v.) significantly cancels chlorpromazine (CPZ)-induced decrease in ventricular fibrillation threshold (VFT). Flavin adenine dinucleotide cancels the effect of CPZ on canine heart mitochondria. After injection of Flavin adenine dinucleotide, the dogs show a transient hypotension within 10 min, then their blood pressures recover to the initial level. Flavin adenine dinucleotide also prevents mitochondrial dysfunction induced by chlorpromazine.