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Background Biochemical markers of inflammation, coagulation and myocardial stress have been associated with both prevalent and incident atrial fibrillation (AF), but little is known about the relationship between biomarker expression and AF burden.Aims Our aim was to investigate the association between cardiovascular biomarkers and AF burden and AF episode duration ≥24 hours.Methods and results In this multicentre observational cohort study, we included 404 patients with paroxysmal AF from the Reappraisal of Atrial Fibrillation: Interaction between Hypercoagulability, Electrical Remodelling and Vascular Destabilisation in the Progression of AF study and evaluated a total of 92 potential cardiovascular blood biomarkers. All patients completed 1 year of follow-up with continuous rhythm monitoring using an implanted loop recorder or a dual-chamber pacemaker. The relationship between biomarker expression and AF was investigated using multiple regression including nine preselected covariates: age, sex, prior heart failure, hypertension, renal insufficiency, prior stroke, coronary artery disease, body mass index and treatment with antiarrhythmic drugs. Elevated levels of N-terminal pro-B-type natriuretic peptide (NT-proBNP) were associated with higher AF burden (incidence rate ratio 1.75, 95% CI 1.75 to 2.06) and AF episode duration ≥24 hours (OR 1.78, 95% CI 1.39 to 2.27). Increased levels of matrix metalloproteinase 2, neurogenic locus notch homologue protein 3 and tumour necrosis factor receptor 2 were additionally associated with AF episode durations ≥24 hours.Conclusions Higher circulating levels of NT-proBNP are associated with increased AF burden and AF episode duration ≥24 hours in patients with paroxysmal AF.Trial registration number NCT02726698.