(AF) occurs in 0.5–1.0% of the general population and in up to 8% of octogenarians,1 2 representing an important cause of stroke.3 Plasma N-terminal pro-brain natriuretic peptide (NTproBNP) levels have been reported to be raised in patients with AF. Successful cardioversion is followed by a rapid decrease in plasma NTproBNP levels in such patients.4–6 Our group has previously shown that, in patients with new-onset AF without symptoms or signs of heart failure, NTproBNP increases rapidly in the plasma, reaching a maximum within 24–36 h, and then decreases even if AF persists, probably due to depletion of atrial pro-natriuretic peptide precursors.7