Objective To compare landiolol and esmolol for treatment of intraoperative arrhythmia in dogs.Methods Experiment Ⅰ Eighty-eight KM mice (44 males, 44 females) , aged 4-6 weeks, were studied.The median lethal dose (LD50) and median effective dose (ED50) of landiolol and esmolol were determined using the sequential method.Treatment index (TI) was calculated.Experiment Ⅱ Eighteen dogs (9 males, 9 females), aged 8-12 months, weighing 7-10 kg, were equally and randomly divided into 3 groups: model group (group M) , landiolol group (group L) and esmolol group (group E).Intraoperative arrhythmia model was established by using gastrointestinal surgery combined with epinephrine.When sustained ventricular arrhythmias occurred, normal saline 0.5 ml/kg, landiolol 8.3 mg/kg and esmolol 10.0 mg/kg were given intravenously in C, L and E groups, respectively.The duration of arrhythmias was recorded.If bradycardia occurred (decrease in heart rate [HR] ≥ 25％ of the baseline value) , isoprenaline 0.05 mg/kg and atropine 0.03 mg/kg were injected intravenously.The occurrence of bradycardia after the initial administration of landiolol and esmolol, and the accumulated dose of landiolol and esmolol consumed when bradycardia occurred were recorded.Isoprenaline and atropine-induced improvement in bradycardia was recorded.Results Compared with esmolol, the LD50 and TI of landiolol were significantly increased (P＜0.01), and no significant change was found in ED50 of landiolol (P＞0.05).The duration of arrhythmias was significantly shorter in L and E groups than in group C, and in group L than in group E (P＜0.01).After the initial administration of landiolol and esmolol, the incidence of bradycardia was 0 and 100％, respectively, and the accumulated dose of landiolol and esmolol consumed when bradycardia occurred was (30± 13) mg/kg.Atropine could not effectively treat bradycardia, while isoprenaline could treat bradycardia.Compared with group L, the time for HR to rise and the duration for HR returning to the baseline value were significantly prolonged in group E (P＜0.05).Conclusion Compared with esmolol, landiolol provides faster improvement in intraoperative arrhythmia, weaker negative chronotropic effect, and higher safety;isoproterenol produces better efficacy in treating landiololinduced bradycardia in dogs.