B-type natriuretic peptide (BNP) is a substance secreted from the ventricles or lower chambers of the heart in response to changes in pressure that happen when heart failure develops and worsens.

The level of BNP in the blood increases when heart failure symptoms worsen and decreases when the heart failure condition is stable. The BNP level in a person with heart failure - even someone whose condition is stable - is higher than in a person with normal heart function.