B-type natriuretic peptide (BNP) is a 32-amino acid polypeptide secreted from the cardiac ventricles in response to ventricular volume expansion and pressure overload. BNP levels are significantly higher in patients with congestive heart failure as compared to patients with respiratory failure due to other causes. Therefore, rapid measurement of BNP might be very helpful in establishing or excluding the diagnosis of heart failure in patients with respiratory failure in the ICU.