An examination was performed in 111 children and adolescents with recurrent and sustained chronic nonparoxysmal tachycardias (CNPT). ECG and electrophysiological studies showed that ante- and retrograde conduction along the accessory atrioventricular junction was the most common mechanisms of arrhythmia. Holter monitoring revealed a high rigidity of cardiac rhythm in patients with sustained CNPT. Criteria for the development of arrhythmogenic cardiac dilatation were developed. In recurrent CNPT, there was a correlation between the paroxysms of ECG slow-wave activity and the "salvos" of tachycardia and a predominance of vagal effects on the heart. A new approach to the treatment of children with CNPT was proposed, which involved the correction of pathogenetic mechanisms. Indications for the usage of antiarrhythmic agents such as cordarone and a cardiac surgeon's advice were formulated. The efficiency of the therapy was achieved in 82% of the children as shown by a follow-up.