BNP (brain natriuretic peptide) belongs to a family of structurally similar peptide hormones, which includes atrial natriuretic peptide (ANP), BNP, C-type natriuretic peptide (CNP) and urodilatin. ANP and BNP act mainly as cardiac hormones, produced primarily by the atrium and ventricle, respectively, while the gene encoding C-type natriuretic peptide is expressed mainly in the brain. BNP circulates in blood as a peptide hormone with natriuretic, vasodilatory and renin inhibitory properties. It is secreted predominantly by the left ventricular myocytes in response to volume expansion and pressure overload. These peptides are characterized by a common 17 amino acid ring structure with a disulfide bond between two cystein residues. This ring structure shows high homology between different natriuretic.