Rapid measurement of BNP is useful in establishing or excluding the diagnosis of heart failure in patients with acute severe shortness of breath. BNP levels can confirm the diagnosis of heart failure when the cause of acute severe shortness of breath remains uncertain after assessment of the history, physical findings, and chest x-ray. The severity of heart failure appears to be reflected by the height of BNP levels. The discovery that A-type (atrial), natriuretic peptide is secreted by the atrium (atrial natriuretic factor), was a major breakthrough that paved the way for the revelation of BNPs.