Idioventricular or accelerated ventricular rhythm has been reported frequently in adults--usually in association with acute myocardial infarction, sometimes in other heart diseases, but also in healthy individuals. Until today the origin of this rhythm disturbance is unknown, its nature benign and doesn't influence the prognosis adversely. The ectopic idioventricular rhythm was present intermittently, competed with the similar frequency of sinus rhythm and subdued by increasing the basic sinus rate was subdued. Such patients needs no therapy! The onset of idioventricular rhythm was observed in infancy and childhood too, but only a few reports exists. One case of idioventricular rhythm occurring in a 9-year-old girl is presented. In our opinion, cardiologic basic diagnostic methods (including echocardiography), Holter monitoring and possibly ergometry are sufficient to characterize this benign rhythm anomaly and to avoid unnecessary and perhaps dangerous treatment with antiarrhythmic drugs.