Final answer:
Brain natriuretic peptide (BNP) is the key diagnostic indicator of heart failure, indicating the heart is under stress unlike BUN and creatinine, which assess kidney function.
Step-by-step explanation:
A key diagnostic indicator of heart failure is Brain natriuretic peptide (BNP). BNP is a hormone produced by your heart's ventricles in response to stretching caused by increased blood volume in these chambers. When the heart detects that it needs to work harder to pump blood, it releases BNP. High levels of BNP can be a sign of heart failure, as they show that the heart is under stress from conditions like hypertension or fluid overload, leading to heart function impairment. Unlike Blood urea nitrogen (BUN) and creatinine, which are primarily used to assess kidney function, BNP specifically aids in diagnosing heart conditions.