An historical outline of antiarrhythmic therapy is presented. At its beginning treatment was based on empirical data and later on electrophysiologic studies; now it is supported on direct knowledge of ionic currents flowing through the cell membrane during different phases of cellular potentials. It has been possible to reach the present stage of knowledge by starting with clinical observations which permitted the introduction of quinidine in therapy, to the choice of specific agents based upon their effects on ionic movements and the mechanisms maintaining active arrhythmias. These mechanisms can be divided into three groups: circus movement, reentry and discharges of ectopic foci. On these bases, it is justified the use of drugs which prolong the refractory period of myocardial fibers in the first group, of those which enlarge the local block in the second and of those which flatten prepotential or depress systolic depolarization in the third.