OBJECTIVES: Postoperative atrial fibrillation (POAF) is a common complication following cardiac surgery. However, knowledge on the rate of long-term atrial fibrillation (LTAF) after POAF remains unclear. We investigated predictors of POAF in patients with aortic stenosis undergoing surgical aortic valve replacement, and assessed the rate of LTAF during follow-up. METHODS: We prospectively included 96 adult patients with severe aortic stenosis undergoing surgical aortic valve replacement. Patients with previous atrial fibrillation (AF) were excluded. Patients underwent echocardiography, cardiac computed tomography and magnetic resonance imaging immediately prior to surgery. Surgical aortic clamp time and postoperative C-reactive protein (CRP) were documented. POAF was defined as AF recorded within 7 days of surgery. Through chart review, patients were followed up for documented episodes of LTAF occurring more than 7 days after surgery. RESULTS: POAF occurred in 51 patients (53%). It was associated with larger preoperative echocardiographic left atrial volume index (44 ± 12 vs 37 ± 8 ml/m2, P = 0.004), longer aortic clamp time [80 (70-102) vs 72 (62-65) min, P = 0.04] and higher CRP on first postoperative day [80 (64-87) vs 65 (44-83) mg/l, P = 0.001]. Multivariable logistic regression revealed that left atrial volume index [odds ratio (OR) 1.07, 95% confidence interval (CI) 1.02-1.13; P = 0.005] and postoperative CRP (OR 1.03, 95% CI 1.01-1.05; P = 0.006) were the only independent predictors of POAF. During 695 days (25th-75th percentile: 498-859 days) of follow-up, LTAF occurred in 11 patients of whom 10 were in the POAF group (hazard ratio 9.4, 95% CI 1.2-74; P = 0.03). CONCLUSIONS: POAF is predicted by left atrial volume index and postoperative CRP. Patients with POAF have a 9-fold increase risk of developing symptomatic LTAF during follow-up. CLINICAL TRIAL REGISTRATION NUMBER: ClinicalTrials.gov (NCT02316587).