320-detector Computed Tomography to Assess Myocardial Extracellular Volume Fraction in Patients With Atrial Fibrillation Before AF Ablation.

Inclusion Criteria:

* Patients must be at least 21 years old at the time of enrollment.
* Patients must be able to give informed consent.
* Patients with symptomatic paroxysmal/persistent atrial fibrillation (AF).
* Eligible patients must be determined to be suitable candidates for ablation to treat AF by their cardiologist and/or electrophysiologists regardless of this protocol.
* Patients are scheduled to have a pre-procedure cardiac CT upon the discretion of their electrophysiologists

Exclusion Criteria:

* Known allergy to iodinated contrast media.
* Elevated serum creatinine (\> 1.5mg/dl) OR calculated creatinine clearance of \< 60 ml/min (using the Cockcroft-Gault formula).
* Patients with a positive urine or serum pregnancy test will be excluded from this study.
* Patients with heart transplantation.
* Patients with polymorphic ventricular tachycardia (VT) or presenting in electrical storm.
* Presence of any other history or condition that the investigator feels would be problematic.
* Patient with iodinated contrast administration for other reason 24 hours prior to investigational CT.
* Patients who have a heart pacemaker, metallic foreign body (metal sliver) in their eye, or who have an aneurysm clip in their brain, mechanical heart valves and prosthetics that contain metal.
* Patients with severe claustrophobia.