The primary objectives are to determine the correlation between rate of temperature decline and nadir cryoballoon temperatures rate of temperature decline and nadir esophageal temperatures during pulmonary vein isolation. To accurately measure the distance between the esophagus and the ostium of each pulmonary vein intra-operatively. To attempt to create recommendations for esophageal temperature-guided ablation in order to increase the safety profile of cryoballoon pulmonary vein isolation (PVI) by providing one center's experience. By trending cryoballoon ablation temperatures and subsequent esophageal temperatures, data trends may emerge and be predictive for esophageal ulceration formation. These trends may include:

• Distance between esophagus and pulmonary vein in patients who developed post-ablation esophageal ulcerations
• Intra-procedure esophageal temperatures in patients who developed post-ablation esophageal ulcerations
• Intra-procedure cryoballoon temperatures in patients who developed post-ablation esophageal ulcerations As well as to associate the development of symptoms (including dysphagia, chest pain, fever, "heartburn," or odynophagia) with the presence of ulcerations.

When treating atrial fibrillation and targeting various areas in the left atrium, electrophysiologists have the choice to perform ablation with RF energy or cryoenergy. Esophageal ulceration and in more rare cases, esophageal fistulae, are known complications of this ablation procedure. Though rare (0.1-0.25% fistula rate and 15-20% esophageal ulceration rate according to the most recent Heart Rhythm Society EHRA ECA consensus statement)1, the investigators would very much like to understand how to completely prevent these occurrences. Cryoenergy has more recently been introduced as an energy source used in the PVI procedure; therefore, for this energy source, rates of esophageal ulceration are not yet well-defined. Nine esophageal fistulae have occurred in the first approximately 130,000 cryoballoon procedures.

Inclusion Criteria:

1. Recurrent, symptomatic, drug-refractory, paroxysmal atrial fibrillation with planned cryoballoon pulmonary vein isolation
2. Age >18 years
3. Planned AF cryoablation procedure

Exclusion Criteria:

1. LA diameter >55mm
2. Severe LVH (LV wall ≥ 15mm)
3. LA thrombus
4. Decompensated heart failure
5. Plans for left atrial ablation lesions beyond isolation of the pulmonary veins
6. History of previous pulmonary vein isolation
7. Inability to place esophageal temperature probe or TEE probe
8. Previously documented phrenic nerve injury
9. Known esophageal pathology (complete GI history worksheet)