Abstract: Abstract Objective To compare cardiaotoxic effect with sparfloxacin and levofloxacin, the effects of antofloxacin on cardiac action potentials were examined. Methods Action potentials were recorded from isolated papillary muscles of guinea pig right ventricles by using conventional microelectrode techniques. Results 1.With stimulation basic cycle length of 1000ms, both APD50 and APD90 were prolonged at any used concentrations by sparfloxacin, While, at the concentrations over 10μmol/L, levofloxacin and antofloxacin prolonged the APD50 and APD90. 2. A the concentrations used by 10μmol/L, antofloxacin prolonged the APD90 were decreased by E-4031, and were increased by Chromanol 293B, no obviously changed by E-4031 and Chromanol 293B.3.With the stimulation basic cycle length increased, the prolongation of APD90 caused by those three drugs were increased，but no frequency dependency. Conclusion: Antofloxacin has less potency to prolong APD as compare to LVFX and SPX, and it maybe prolong APD by inhabit IKr.