Introduction: The invasive therapeutic approach of the tachyarrhythmia in young children is encumbered by numerous controversies. This paper aims to demonstrate the benefit of radical treatment by radiofrequency catheter ablation (RFA) performed after electrophysiological study (EPS) in children weighting less than 20 kg, in the light of balance modulation between efficiency and procedural complications. Methods: A total of 934 children with arrhythmia evaluated by EPS and treated by RFA were admitted between Nov 1998 and May 2014 in the IBCV Timișoara. Out of these, 131 children (14.02%) had a weight of maximum 20 kg. Evaluation of these children by EPS re vealed: WPW sd. – 37 patients (p) (28,24%), hidden accessory pathways (AP) – 34 p (25,95%), AVNRT – 39 p (29.77%), permanent junctional orthodromic reciprocal tachycardia with dilated rhythmic cardiomyopathy – 5 p (3.81%), Mahaim sd. – 2 p (1.52%), atrial flutter – 1 p (0.76%), permanent atrial tachycardia – 4 p (3.05%), reentrant scar tachycardia aft er surgical correction of congenital disease – 3 p (2.29%), complex tachycardia associated with congenital diseases – 3 p (2.29%), idiopathic fascicular VT – 1 p (0.76%), VT of right ventricular outfl ow tract – 2 p (1.52%). Results: RFA was performed from 10 kg (min. 2 years old) to prevent progression and extension of cardiac scars described after ablation on the developing heart. Th ere have been used small diagnostic 5 Fr catheters and 6 Fr ablation catheters having a suitable structure to prevent tissue trauma. Ablation applications were short (up to 15 – 20 seconds), with low energies between 20 and 25W. Manipulation of the catheter and positioning were carried out in a gentle manner in order to do no damage to the ventricular chordae. The success rate was 97.7%, a number of 3 children requiring re-intervention. There were no bleeding complications. Avoiding unnecessary loss of blood was aimed because loss of more than 20 ml of blood in children may require transfusion. There were no procedural complications. Conclusions: The RFA is considered a highly curative method and will be used with caution in children younger than 2 years when the medication has failed or when the instability of the subjacent arrhythmia is life-threatening. Given that most arrhythmias encountered in pediatric patients are among the most curable, the RFA can be tempted with great caution, appropriate materials and energy and fine and gentle maneuvers. One must keep in mind that the heart of a child of 20 kg is different in terms of tissue fragility and sometimes by the relations between the various structures (the relation between the atrioventricular ring and the coronary arteries, for example). On the other hand, a properly done RFA may cure the patient. The dilated rhythmic cardiomyopathy appeared at that age is completely reversible.