Reactive oxygen species, generated and released during digoxin-induced cardiotoxicity, can produce an activation of poly (ADP-ribose) synthase (PARS). Our objective was to examine the effects of PARS inhibitors, 3-aminobenzamide (3-AB) and nicotinamide, on digoxin-induced arrhythmias in guinea-pig isolated hearts. 3-AB (0.1-0.3 mM) and nicotinamide (0.3 mM) were added to the perfusion solution starting 10 min before digoxin infusion (8 mug ml(-1) min(-1) reaching the heart) and maintained throughout the experiments. Electrocardiograms and coronary perfusion pressure were recorded continuously, and digoxin-induced arrhythmias were determined. Nicotinamide markedly inhibited ventricular tachycardia (VT) incidence (from 100%, n = 7, to 29%, n = 7), and abolished ventricular fibrillation (VF) incidence. 3-AB (0.1 mM, n = 9) significantly decreased VT incidence from 100% (n = 7) to 22% (n = 9) and VF incidence from 86% (n = 7) to 11% (n = 9). Both nicotinamide and 3-AB (0.1 mM) markedly decreased number of ventricular ectopic beats (VEBs) and arrhythmia score. 3-AB at 0.3 mM (n = 8) appeared to decrease the VT (to 63%) and VF incidence (to 38%), but these reductions did not reach statistically significance levels. Moreover, 3-AB at high concentration (0.3 mM) did not significantly modify the number of VEBs and arrhythmia score. There were no significant changes in coronary perfusion pressure, heart rate or pressure rate index measured at certain time points throughout the experiment in all groups. Our results suggest that PARS activation plays a role in the digitalis-induced cardiotoxicity in guinea-pig isolated hearts. (C) 2002 Elsevier Science Ltd.