The effects of 3-(diisopropylaminoethylamino)-2',6'-dimethylpropionanilide (AN-132), a new antiarrhythmic drug, on the electrical activities of dog ventricular muscles and Purkinje fibers were studied using standard microelectrode techniques. In ventricular muscles, AN-132 (10(-5)-10(-4) mol/l) decreased the overshoot potential and the maximum rate of rise of the action potential without changing the resting membrane potential, the plateau potential and the action potential duration at a driving rate of 0.5 Hz. These results indicate that AN-132 belongs to class 1 antiarrhythmic drugs. Lidocaine (10(-6)-10(-4) mol/l) failed to affect these parameters under the same conditions. In Purkinje fibers, both drugs decreased the plateau potential and shortened the action potential duration. To subclassify AN-132 among class 1 antiarrhythmic drugs, the kinetics of onset of rate-dependent effect of AN-132 (10(-4) mol/l) was compared with that of lidocaine (10(-4) mol/l), and AN-132 was found to have the slower onset kinetics than lidocaine.