Three-dimensional (3-D) mapping systems are of great value for the diagnosis and ablation of cardiac arrhythmias. If applied appropriately, 3-D mapping systems (3DM) can reduce fluoroscopy and procedural time. In general, two advanced mapping systems are currently in use: the Carto™ system (Biosense Webster) uses ultralow-intensity magnetic fields to locate specially designed catheters in the heart chamber. Both, the activation sequence (activation map) and the local potential amplitude (voltage map) can be displayed. Additional applications are available: the SmartTouch™ Catheter offers contact force registration, while CartoMerge™ enables integration of other imaging modalities into the map. The other commonly used mapping system is EnSite NavX™(Endocardial Solutions, St. Jude), which uses electrical current delivered across different pairs of patches on the body surface, and thereby creating voltage gradients. Thus, catheter tips and shafts in a 3-D field can be localized. Special applications of this system are the automated registration of complex fractionated atrial electrograms (CFAE) and a non-contact mapping function using the EnSite Array™ Mapping system. The EnSite-NavX™ system is not limited to the use of special sensor-equipped catheters. Basically, both systems are compatible with the remote navigation systems "Niobe™" and "Sensei®.