MRI produces images that serve as luminal, edema, & scar maps to assist in the Electrophysiological (EP) treatment of ventricular and atrial arrhythmias . Until MR-compatible EP devices are widely available, there will be a need to perform EP partially in the MRI for imaging, and partially outside the MRI for ablation, puncture & navigation. An MR-conditional voltage-based Electroanatomic Mapping (EAM) system would allow MR-guided EP in MRI & registration-free EP to be performed outside the MRI during X-ray, Intra-Cardiac-Echo (ICE) or EAM guidance. Previously a 1.5T MR-conditional St. Jude Medical EnSite Velocity (Velocity) voltage-based EAM system was presented . The study objective was to conduct a multi-catheter registration free EAM (localization & intra-cardiac Electrogram (EGM) measurement) both in & outside of the MRI.