PURPOSE: To prospectively determine the impact of sinus rhythm restoration on left-atrial (LA) volumes and function assessed by cardiac magnetic resonance (CMR) imaging within the first year after pulmonary vein isolation (PVI). METHODS: Forty-one patients (28 men; age: 57±10years) with paroxysmal or non-paroxysmal atrial fibrillation were studied serially using CMR at baseline and at 1-, 3-, 6- and 12-month intervals following PVI. LA diastolic and systolic volumes were determined by cine imaging with full gapless LA coverage applying Simpson's rule. Successful PVI was defined by a persisting sinus rhythm during the 12-month follow-up after a 3-month blanking period; patients with a relapse of atrial fibrillation after the blanking period were censored (4 patients at 6-month follow-up and additional 6 patients at 12-month follow-up). RESULTS: In all patients, LA diastolic and systolic volumes decreased significantly and progressively during the 12-month follow-up (p<0.001 and p=0.001, respectively). At baseline patients with successful PVI demonstrated a significantly smaller LA diastolic volume compared to patients with relapsed atrial fibrillation (p=0.009). During the 3-month blanking period, patients with successful PVI showed a significant decrease of LA diastolic and systolic volumes (p=0.026 and p=0.006, respectively) and a significant increase of LA ejection fraction (p=0.028); patients with subsequent relapse of atrial fibrillation, however, exhibited no significant change of LA diastolic and systolic volumes or LA ejection fraction. CONCLUSION: Restoration of sinus rhythm led to a significant and progressive decrease of left-atrial diastolic and systolic volumes during one year following pulmonary vein isolation.