Background The concentrations of atrial and brain natriuretic peptides (ANP and BNP) are elevated in patients with atrial fibrillation (AF), but the usefulness of their measurement before and after AF ablation has not been reported. Methods and Results The concentrations of the natriuretic peptides were evaluated in 54 patients undergoing catheter ablation for drug-resistant paroxysmal and persistent AF without heart failure. Based on the outcome, the patients were divided into 2 groups: successful (n=42) or failure (n=12). All patients were asked to keep a log of the duration and frequency of their symptoms and underwent 24-h ECG monitoring at least once after the ablation. The plasma BNP and ANP concentrations, most of which were well below the heart failure range, exceeded the normal range in 69% and 26% of the patients, respectively. The BNP concentration decreased after ablation in the success group (49±43 to 27±28 pg/ml; p<0.05), however, it was unchanged in the failure group (46±35 to 70±37 pg/ml; p=0.46). A value of the ΔBNP (BNP after ablation - BNP before ablation) of ≤0 pg/ml identified a successful ablation with a sensitivity of 83% and specificity of 83%. The plasma ANP concentration did not differ statistically between the 2 groups before and after the ablation. Conclusion A moderate elevation in the BNP concentration is often found in patients with symptomatic paroxysmal and persistent AF, and a reduction in the plasma BNP concentration shortly after the ablation may indicate a successful outcome. (Circ J 2007; 71: 313 - 320)