Brain natriuretic peptide levels (BNP) have been best studied in the heart failure (HF) literature and has been increasingly used in the critical care population as an estimate of cardiac function. BNP is secreted by cardiomyocytes in response to an increase in transmural ventricular pressure. The measurement of BNP is well known in the cardiac literature. Studies in the critical care population have looked at measuring BNP in different subsets of patients with sepsis, pulmonary embolism (PE), acute respiratory distress syndrome (ARDS), pulmonary hypertension (PH) and non-cardiogenic pulmonary edema (CPE). BNP has been used to differentiate HF syndrome from other causes of respiratory failure both in the acute and chronic settings. The measurement of BNP in the critical care population is fraught with difficulties only one of which is the significant effect of renal failure on our ability to interpret BNP levels effectively. This review summarizes the current literature on the utility and significance of measuring BNP in the critical care population.