Introduction: The impact of atrial natriuretic peptide (ANP) value for predicting paroxysmal atrial fibrillation (pAF) in ischemic stroke patients remains uncertain. Methods: The consecutive 222 ischemic stroke patients (median 77 [IQR 68-83] years old, 93 females) within 48 hours after onset were retrospectively studied. Plasma ANP and brain natriuretic peptide (BNP) levels were simultaneously measured at admission. Of all, 158 patients had no evidence of atrial fibrillation (AF) (sinus rhythm [SR] group), 25 patients had pAF (pAF group), and the other 39 patients had chronic AF (cAF group). We investigated predicting factors for pAF, with focus on ANP, BNP, and ANP/BNP ratio. Results: ANP value was significantly higher in the pAF than in the SR group (97 [50-157] mg/dL versus 42 [26-72] mg/dL, P < .05) and further increased in the cAF group (228 [120-392], P < .05 versus pAF and SR groups). Similarly, the BNP value was higher in the pAF than in the SR group (116 [70-238] mg/dL versus 34 [14-72] mg/dL, P <.05) and further increased in the cAF group (269 [199-423], P < .05 versus pAF and SR groups). ANP/ BNP ratio was lower in the pAF and cAF groups than in the SR group (. 6 [. 51.2] and.7 [.5-1.0] versus 1.3 [. 8-2.4], both P < .05]. Multivariate analysis in the SR and pAF groups (n = 183) demonstrated that age, congestive heart failure, ANP, and BNP, but not ANP/BNP ratio, were independent predictors for detecting pAF. Receiver operating characteristic curve analysis further showed that area under the curve was similar between ANP and BNP (. 76 and .80). Conclusions: ANP may be clinically useful for detecting pAF in ischemic stroke patients as well as BNP. (C) 2017 National Stroke Association. Published by Elsevier Inc. All rights reserved.