1. The effects of a lipoxygenase inhibitor, BW A4C, on digoxin-induced arrhythmias and cardiac dynamics (contractile force, perfussion pressure, heart rate) were investigated in Langendorff perfused isolated guinea pig hearts. In the control group, arrhythmias were induced by 25 mu g/ml digoxin at a perfusion rate of 0.5 ml/min. In the treated groups, BW A4C (1 and 0.3 mu M) perfused continuously from 15 min prior to digoxin until cardiac arrest occurred. Digoxin exposure (mu g/g wet weight of heart) for the occurrence of arrhythmias and cardiac arrest were the parameters evaluated to assess cardiotoxicity.