['Pulmonary vein reconnection after pulmonary vein isolation is common and is usually associated with recurrences of atrial fibrillation. We used cardiac magnetic resonance imaging after radiofrequency ablation to investigate the hypothesis that acute pulmonary vein isolation results from a combination of irreversible and reversible atrial injury.', 'Delayed enhancement (DE; representing areas of acute tissue injury/necrosis) and T2-weighted (representing tissue water content, including edema) cardiac magnetic resonance scans were performed before, immediately after (acute), and later than 3 months (late) after pulmonary vein isolation in 25 patients with paroxysmal atrial fibrillation undergoing wide-area circumferential ablation. Images were analyzed as pairs of pulmonary veins to quantify the percentage of circumferential antral encirclement composed of DE, T2, and combined DE+T2 signal. Fourteen of 25 patients were atrial fibrillation free at 11-month follow-up (interquartile range, 8-16 months). These patients had higher DE (71±6.0%) and lower T2 signal (72±7.8%) encirclement on the acute scans compared with recurrences (DE, 55±9.1%; T2, 85±6.3%; P<0.05). Patients maintaining sinus rhythm had a lesser decline in DE between acute and chronic scans compared with recurrences (71±6.0% and 60±5.8% versus 55±9.1% and 34±7.3%, respectively). The percentage of encirclement by a combination of DE+T2 was almost similar in both groups on the acute scans (atrial fibrillation free, 89±5.4%; recurrences, 92±4.8%) but different on the chronic scans (60±5.7% versus 34±7.3%).'] Is acute pulmonary vein isolation achieved by a combination of reversible and irreversible atrial injury after catheter ablation : evidence from magnetic resonance imaging?