Radiofrequency (RF) catheter modification of the sinus node appears to be a promising therapeutic modality for the treatment of inappropriate sinus tachycardia. Modification, as opposed to total obliteration, of the atrial pacemaker requires precise localization of the sinus node. This has been successfully achieved with a multicatheter approach guided by intracardiac echocardiography. This article describes the first clinical use of a tridimensional nonfluoroscopic mapping system to guide successful RF modification of the sinus node in two cases of inappropriate sinus tachycardia. This system simplifies the current approach and greatly reduces the fluoroscopy time.