To test the hypothesis that localized functional reentry maintains Afib in humans, ibutilide will be administered intravenously in patients undergoing an Afib ablation. The hypothesis of this study is that ibutilide will decrease the high frequency signals observed in Afib suggesting the presence of micro reentrant circuits as the basic mechanism of Afib, especially for the paroxysmal Afib group. The potential difference in response to the ibutilide in patients with paroxysmal versus persistent Afib may show the difference in the underlying mechanism of Afib between these two groups.

Inclusion Criteria:

• patients to be scheduled for atrial fibrillation radio frequency ablation
• paroxysmal, permanent symptomatic atrial fibrillation refractory to conventional treatment
• symptomatic atrial fibrillation that do not want or desire to take medication or undergo cardioversion
• patients on antiarrhythmics that can be discontinued 5 half lifes prior to the procedure except for Amiodarone

Exclusion Criteria:

• patients with recent major hemorrhage (within 6 months)
• patients with a coagulopathy
• patients who are pregnant or breast feeding
• patients with acute congestive heart failure
• patients with hypokalemia or hyperkalemia
• patients with a prolonged QTc > 440mms
• patients with polymorphic ventricular tachycardia secondary to antiarrhythmic class III and class I
• patients with left ventricular dysfunction < 40%
• patients with a history of recent MI (< 1 month)
• patients with a history of an angioplasty of < 1 month
• patients with a history of coronary artery bypass grafting surgery of < 3 months.
• patients with a history of chronic renal failure or a creatinine clearance of < 30ml/m
• patients with a history of stroke of < 6 months