 An objective of the study is to perform the entire ablation procedure from subject preparation through confirmation of bidirectional conduction block entirely under magnetic resonance guidance. However, at the investigators discretion, the preparation of the subject may occur in a conventional electrophysiology laboratory followed by transferring the patient to the magnetic resonance suite for the ablation procedure. Additionally, if bidirectional conduction block is not achieved within 90 minutes from the initial catheter placement, the subject may be transferred from the magnetic resonance suite to a conventional electrophysiology lab to complete the procedure. Clinical success is bidirectional conduction block regardless of the environment within which the ablation occurs. 