Dilated cardiomyopathy induces circulatory insufficiency with poor prognosis. Persistent tachyarrhythmias may be the cause of this disease. At particular high risk for heart damage and insufficiency are young people and children. The group of most dangerous arrhythmias consist of: incessant tachycardia in patients with preexcitation syndrome and supraventricular tachyarrhythmias (atrial flutter and fibrillation, ectopic atrial tachycardia) with high rate of ventricles. The result of arrhythmias is dilatation of the heart and thinness of ventricular walls with hemodynamic disorders. The effective therapy of arrhythmias--ablation of the accessory pathway in patients with pre-excitation syndrome or reversion to sinus rhythm (pharmacological or electric cardioversion) in patients with atrial fibrillation and flutter, often leads to normalisation of heart ejection function and diameter. Therefore it exist important question: is dilated cardiomyopathy the cause or consequence of tachyarrhythmias? Causative antiarrhythmic therapy in these second cases gives a possibility to improve the prognosis in patients with such a disease.