patient is at least 18 years old.

patient is undergoing an atrial fibrillation ablation procedure.

patient has a transesophageal echocardiogram (tee) within the 48 hours prior to ablation procedure to rule out left atrial thrombus.

patient provides informed, written consent for participation in the study.

patients in whom placement of an ice catheter in the right atrium for adequate atrial visualization is not technically feasible (as evaluated and determined by the physician performing the procedure).

patients in whom transseptal puncture is relatively contraindicated.

patients in whom left atrial clot or dense spontaneous contrast is identified on tee, which would increase thromboembolic risk.

women of child bearing potential, in whom pregnancy cannot be excluded.

patients unable to grant informed, written consent for participation in the study.