Abstract: A transseptal puncture system and method uses a guiding instrument, and an atraumatic puncture instrument longitudinally movable therein, with a first electrode configured for ablation and a second electrode electrically insulated from the first electrode. An impedance monitoring module is configured to measure at least an impedance at the second electrode, and an electrical generator is configured to selectively apply electrical energy to the first electrode based at least in part on the measured impedance at the second electrode. Moreover, impedance measurements at the first and second electrodes are used to determine relative positions of the instruments in the approach, contact, ablation and puncture of the septum.