The purpose of this study is to assess the safety and performance of the Hansen Medical Sensei Robotic System and Artisan Catheter when used to robotically manipulate the Biosense ThermoCool ablation catheter for the treatment of atrial fibrillation (irregular heartbeats originating in the upper chambers of the heart). The Biosense ThermoCool catheter is FDA approved for use in ablation therapy. The Hansen Medical Robotic Sensei System and Artisan catheter is approved in Europe for use during ablation procedures. This system has been used to treat atrial fibrillation in over 1000 patients worldwide by navigating existing, approved ablation catheters. In the US the Hansen Sensei System with Artisan catheter has FDA clearance as a robotic delivery system to facilitate manipulation, positioning and control of catheters used to collect electrophysiological data within the heart atria (upper chambers or the heart) but has not been studied or approved in the US for use in ablation treatment This study is looking to show safety, compatibility and effectiveness when the Hansen system is used in conjunction with the ThermoCool ablation catheter in the treatment of atrial fibrillation. This will be done by to either treatment with manual delivery of the ThermoCool ablation catheter or treatment with robotic delivery of the of the ThermoCool ablation catheter.