BNP:Natriuretic Pept. :blood natriuretic peptide. This is a substance hormone-like created in the heart that gets elevated in congestive heart failure and during heart attacks. It is used in conjunction with the clinical signs to monitor pts with congestive heart failure. Higher-than-normal results suggest that a person is in heart failure, and the level of bnp or nt-probnp in the blood is related to the severity.