Plasma concentration of brain natriuretic peptide (BNP), as measured by the Triage BNP Test, is approved by the Food and Drug Administration to aid in the diagnosis of heart failure. This diagnostic test is available in many institutions. The purpose of this article is to help the physician know the appropriate time to order this test and to aid in interpreting results. To achieve this goal, we review the physiology of BNP, clinical studies that support its use for diagnosing heart failure, and confounding variables to consider when BNP is being used clinically. We show that the BNP test can be extremely helpful when used in the correct clinical setting.