Brain natriuretic peptide (BNP) is a protein that is produced by the muscles of the heart (particularly left ventricle) in response to a variety of stimuli. Its level in the blood (or plasma, P-BNP) correlates with the presence and severity of heart failure. It is thus used to diagnose & assess severity of heart failure and to monitor the response to treatment. The biological reference interval varies from laboratory to laboratory but generally a value of less than 100 pg/ml is taken to be normal. Its level varies with age, sex, body mass index and genetic factors with higher levels being seen in the elderly & women. An elevated BNP in heart failure falls following treatment. You need to discuss the report with your doctor who will be best placed to advise.