In order to compare and clarify the effects of various antiarrhythmic drugs, we examined drug effects on several canine arrhythmia models, simultaneously determining the minimum effective plasma concentrations. We used 1) two-stage coronary ligation arrhythmia, 2) digitalis arrhythmia, and 3) halothane-adrenaline arrhythmia. The following are, a summary of our results : Antiarrhythmic drugs of class 1 all suppressed digitalis arrhythmia, and except for lidocaine, also suppressed coronary ligation arrhythmia. Class 2 antiarrhythmic drugs, β blockers, and class 4 antiarrhythmic drugs, Ca channel blockers, had common features of effectiveness, where they suppressed adrenaline arrhythmia in relatively low concentrations. Some differences among the antiarrhythmic effects of class 1 drugs could not be explained by their subclassification based either on action potential duration or kinetic properties of dissociation or association with Na channels. A new arrhythmia model for triggered activity in in vivo canine heart was developed, but drug effects on it does not seem to be very different from the effects on the other three arrhythmia models.