B-type natriuretic peptide (BNP) is increasingly being used as a diagnostic marker in the diagnosis of heart failure. Here we evaluate the evidence base for its utility in the ED. Clinical trials suggest that it is more accurate than clinical acumen especially when emergency physicians have diagnostic problems. BNP appears more accurate than any clinical findings or radiological signs. In conjunction with considered clinical judgement, knowledge of its limitations and variable cut-off points, BNP can be of considerable utility to the emergency physician.