A patient with severe tricyclic antidepressant poisoning who showed recurrent ventricular fibrillation and wide QRS complexes on the ECG, failed to respond to intravenous physostigmine and lidocaine. Deliberate artificial hyperventilation was immediately effective in preventing further arrhythmia and in decreasing the width of the QRS complexes. Hyperventilation, a neglected treatment, may be immediately effective in the treatment of severe tricyclic antidepressant poisoning.