Intravenous doses of 2.5 mg/kg and 5.0 mg/kg of levamisole on RR, QT, QTc (corrected QT), and heart rate in conscious rabbits were evaluated. The study was performed on 14 New Zealand rabbits, 1 year old, weighing between 2.5-3 kg. The animals were assigned to 2 equal groups. Rabbits of groups I and II received via the auricular vein 2.5 mg/kg and 5 mg/kg of levamisole HCl, respectively. Alligator clips were attached to four limbs. ECG records were taken by direct writing electrocardiograph before the study and after 2, 4, 6, 8, 10, 15, and 20 min of the experiment. The QT interval was manually calculated from the beginning of Q wave to the end of T wave. The same leads (II and aVR) were selected for all QT interval measurement. The animals were not given any sedatives or anaesthetics before and during ECG recording. In group I, two rabbits had the second degree atrial block at the 2(nd) and 4(th) min after the injection, which disappeared later. Heart rates were 216-230 beats/min at min 0 and dropped to 193-210 beats/min at the 2(nd) min after the injection in both groups, and remained low throughout the study. Heart rates of both groups taken at 2, 4, 6, 8, 10, 15, and 20 min after the injection were significantly lower than the values taken at 0 min except for the values of the 15(th) min in group II. QT and QTc prolongation was noticed in both groups when compared to 0 min values. Although we have no solid data to explain the mechanism involved in bradycardia and atrial block provoked by levamisole, its use resulted in bradycardia, second-degree atrial block, and acute prolongation of QT and QTc in conscious rabbits.