The effect of fluvoxamine (FLV) a selective serotonin reuptake inhibitor agent was studied on ouabain-induced arrhythmia in spontaneously beating isolated guinea-pig atria. FLV (8–64μM) caused a dose-dependent decrease in the rate of contractions (7–52%) and in the contractile force (11–57%). Ouabain alone (2μM) produced arrhythmia at 4.6min and asystole at 17.4min. Pre-administration of the atria with FLV (32μM) significantly increased the time required to produce arrhythmia by ouabain to 14.6min, prolonged the beating of atria to more than 58.6min and delayed the occurrence of asystolia. The pattern of contractile force induced by FLV+ouabain was more regular than that produced by ouabain alone. These findings indicate that FLV produces direct cardiac action, probably due to the inhibition of cardiac Na + and Ca 2+ channels. Our results suggest that FLV may reduce the membrane conduction through inhibition of ionic channels which decrease ouabain-induced arrhythmia.