In the present study, the possible role of oxygen-derived free radicals (OFR) on digoxin- (0.6 mg/kg(-1) IV bolus) induced arrhythmias of anesthetized guinea-pigs has been investigated. Guinea-pigs (300-400 g) of either sex were anesthetized with urethane (1.5 g/kg(-1), IF), and their trachea for respiration,left common carotid artery for blood pressure monitoring, and right jugular vein for drug administration were cannulated. ECG and haemodynamics were recorded throughout the experiments. None of the agents used [N-acetyl-L-cysteine (20 mg/kg(-1) IV bolus), or SOD (30,000 IU/kg(-1) IV bolus) + catalase (15,000 IU/kg-1 IV bolus)] significantly inhibited the arrhythmias except desferrioxamine which reduced the incidence of ventricular fibrillation and arrhythmia score. Desferrioxamine, by acting intracellularly unlike other agents used, might prevent the reduction of Fe+3 by ascorbate and superoxide anion thus inhibiting the formation of cytotoxic hydroxyl radical in this experimental setting. (C) 1999 Elsevier Science Inc. All rights reserved.