Angiotensin-(1-5) [Ang-(1-5)], which is a metabolite of Angiotensin-(1-7) [Ang-(1-7)] catalyzed by angiotensin-converting enzyme (ACE), is a pentapeptide of the renin-angiotensin system (RAS). It has been reported that Ang-(1-7) and Ang-(1-9) stimulate the secretion of atrial natriuretic peptide (ANP) via Mas receptor (Mas R) and Ang II type 2 receptor (AT2R), respectively. The effect of Ang-(1-5) on ANP secretion was investigated using isolated perfused beating rat atria. Ang-(1-5) stimulated high pacing frequency-induced ANP secretion in a dose-dependent manner. Ang-(1-5)-induced ANP secretion was attenuated by the pretreatment with an antagonist of Mas R (A-779) but not by an antagonist of AT1R (losartan) or AT2R (PD123,319).