Aim:Overdoses of haloperidol are associated with major ventricular arrhythmias,cardiac conduction block,and sudden death.The aim of this experiment was tostudy the effect of haloperidol on the action potentials in cardiac Purkinje fibersand papillary muscles under normal and simulated ischemia conditions in rabbitsand guinea pigs.Methods:Using the standard intracellular microelectrodetechnique,we examined the effects of haloperidol on the action potential param-eters[action potential amplitude(APA),phase 0 maximum upstroke velocity(V_(max)),action potential amplitude at 90% of repolarization(APD_(90)),and effective refrac-tory period(ERP)]in rabbit cardiac Purkinje fibers and guinea pig cardiac papillarycells,in which both tissues were under simulated ischemic conditions.Results:Under ischemic conditions,different concentrations of haloperidol depressed APAand prolonged APD_(90)in a concentration-dependent manner in rabbit Purkinjefibers.Haloperidol(3μmol/L)significantly depressed APA and prolonged APD_(90),and from 1μmol/L,haloperidol showed significant depression on V_(max);ERP wasnot significantly affected.In guinea pig cardiac papillary muscles,the thresholdsof significant reduction in APA,V_(max),EPR,and APD_(90)were 10,0.3,1,and1μmol/L,respectively,for haloperidol.Conclusion:Compared with cardiac con-ductive tissues,papillary muscles were more sensitive to ischemic conditions.Under ischemia,haloperidol prolonged ERP and APD_(90)in a concentration-depen-dent manner and precipitated the decrease in V_(max)induced by ischemia.Theshortening of ERP and APD_(90)in papillary muscle action potentials may be inhibi-ted by haloperidol. Aim: Overdoses of haloperidol are associated with major ventricular arrhythmias, cardiac conduction block, and sudden death. The aim of this experiment was tostudy the effect of haloperidol on the action potentials in cardiac Purkinje fibers and papillary muscles under normal and simulated ischemia conditions in rabbits and guinea pigs.Methods: Using the standard intracellular microelectrodetechnique, we examined the effects of haloperidol on the action potential param-eters [action potential amplitude (APA), phase 0 maximum upstroke velocity (V_ (max)), action potential amplitude at 90% of repolarization (APD_ (90)), and effective refrac-tory period (ERP)] in rabbit cardiac Purkinje fibers and guinea pig cardiac papillary cells, in which both both tissues were under simulated ischemic conditions. Results: Under ischemic conditions, different concentrations of haloperidol depressed APA and prolonged APD_ (90) in a concentration-dependent manner in rabbit Purkinjefibers. Haloperidol (3 μmol / L) significantly depressed APA and prolonged APD_ (90), and from 1 μmol / L, haloperidol showed significant depression on V_ (max); ERP wasnot significantly affected in. guinea pig cardiac papillary muscles, the thresholds significant reduction in APA, V max, EPR, and Conclusions: Compared with cardiac con-ductive tissues, papillary muscles were more sensitive to ischemic conditions.Under ischemia, haloperidol prolonged ERP and APD_ (90), APD_ (90) were 10,0.3,1, and1μmol / in a concentration-depen-dent manner and precipitated the decrease in V max (max) induced by ischemia.Theshortening of ERP and APD_ (90) in papillary muscle action potentials may be inhibi- ted by haloperidol.