Proteins the heart releases when it’s under stress — used as blood tests to diagnose heart failure and track disease severity.B-type natriuretic peptide (BNP) and its cleavage product NT-proBNP are among the most important cardiac biomarkers in clinical medicine. Nesiritide (Natrecor) is recombinant BNP — the same molecule used as a biomarker repurposed as a therapeutic to dilate blood vessels in acute decompensated heart failure. The ASCEND-HF trial showed nesiritide improved dyspnea but not mortality or re-hospitalization — a reminder that biomarker improvement and clinical benefit are not the same thing.