Prologation of the corrected QT(QTc) has been shown to increase the period of vulnerability of the heart to arrhythmias as well as to increase the incidence of ventricular premature beats. Previous studies indicate that inhalation anesthetics may prolong the QTc interval, because of the decrease in slow channel-medicated current. Therefore this study was performed to evaluate the effects of halothane and/or intervals in the cat. Adult male of female cats weighing 2-4kg were divided into verapamil-treated group(group l), halothane-treated group(group lla) and halothane-and verapamil-treated group(group llb). The QTc blood pressures and heart rates were measured with EKG lead ll to compare those at pretreatment with at post-treatment. The results are follows: 1) The QTc intervals at the post-treatment period are significantly longer than those at the pre-treatment period in all groups(p<0.05). 2) In group ll, the systolic and diastolic blood pressures, and the heart rates after administration were decreased(p<0.05). 3) the QTc intervals in group llb were more prolonged than in group lla(p<0.05). 4) No correlation between thredd different doses of verapamil and the degree of prolongation of QTc intervals was shown. It was concluded that either halothane or verapamil prolonged the QTc intervals and simultaneous administration of both agents resulted in even more prolongation of QTc intervals. However, the size of dose of verapamil was not related to the degree of prolongation of QTc intervals.