Organophosphate poisoning causes disturbances in cardiac conduction and potentially fatal severe cardiac rhythm abnormalities. This study investigated the cardiac effects of atropine and pralidoxime in the treatment of organophosphate poisoning in rats. Three groups of 10 adult male Wistar rats were anesthetized with an intraperitoneal injection of ketamine 100 mg/kg and xylazine 10mg/kg and connected to a computerized electrocardiographic monitor. Each rat was then injected intraperitoneally with the pesticide clichlorvos 70 mg/kg. Sixty seconds after the injection, 10 rats were injected with saline, 10 with pralidoxime mesylate 20 mg/kg, and 10 with atropine 10 mg/kg. During the computerized electrocardiographic monitoring, each rat's heart rate and QT(c) intervals were recorded and analyzed as the injections were administered. The heart rates in all 3 groups did not differ before the dichlorvos was administered, nor at 60 seconds afterward, but in the atropine group, the time elapsed before the first decline in heart rate was significantly longer than that in the control group (P < .05). In addition, the interval before death was significantly longer in the atropine group than in either the control group or the pralidoxime group (P < .05 for both). The QT(c) was almost identical in each of the groups. Atropine has beneficial effects on the heart rate prolongs the time before the heart rate declines, and delays death but has no effect on the QT(c) interval. Further research about the toxic effects of organophosphate compounds on myocardial cells is warranted.