B-type natriuretic peptide (BNP) has emerged as a reliable biomarker in patients with congestive heart failure. The mature, biologically active B-type natriuretic peptide, BNP(1-32), is cleaved by corin from the 108 amino acid proBNP. However, in vivo as well as in vitro data demonstrated that this BNP(1-32) might be an ideal substrate for the endogenous aminopeptidase, dipeptidyl-peptidase IV (DPP IV). DPP IV removes the two amino terminal amino acids (Ser Pro) from BNP(1-32) to produce BNP(3-32), which has been detected in plasma of patients with congestive heart failure. The biological effects of BNP(3-32) remain undetermined. In cultured human cardiomyocytes and fibroblasts, equimolar concentrations of BNP(1-32) and BNP(3-32) both exert similar biological effects, as evidenced by their cGMP (cyclic guanylate monophosphate) generating capacity. However, in a canine model, intravenous BNP(3-32) infusion resulted in less natriuresis, diuresis, and vasodilation compared to intravenous infusion of BNP(1-32). The clinical relevance of these observations might be important for patients in whom the plasma BNP concentrations, measured by commercially available immunoassays, are high. Further studies exploring whether DPP IV inhibitors increase the bioavailability of BNP(1-32), delay the progression of heart failure, and increase the efficacy of exogenous administration of BNP(1-32) in decompensated heart failure are needed.