The aim of this work is to summarize the first experience in Chile modifying the slow pathway in patients with tachycardias due to atrio-ventricular node reentry. Until now, the only available treatment was the use of antiarrhythmic drugs. The radiofrequency fulguration or cauterization of part of the atrioventricular node has been reported as a treatment for these arrhythmias. The initial technique fulgurated the rapid pathway with a significant risk of atrioventricular block. The modification of the slow pathway has been recently described. We report two patients, 9 and 45 years old, with a history of recurrent tachycardias, refractory to pharmacological treatment. An electrophysiological study demonstrated that the mechanism of their arrhytmias was a nodal reentry. In the same session one of the mapping catheters was changed by a fulguration one and radiofrequency was applied, using a variation of the technique described by Jackman. In both, the slow plathway was modified or blocked with definitive interruption of the nodal reentry circuit and preservation of atrioventricular conduction.