A simple blood test useful to the diagnosis and follow-up of congestive heart failure would have a favorable impact on the management of a large populations of patients. Several recent studies have demonstrated that blood levels of Brain Natriuretic Peptide (BNP) may be useful for differentiating heart failure from lung disease in patients presenting to emergency department with dyspnea. Furthermore, BNP might serve as screening test for left ventricular dysfunction (systolic and diastolic), correlates with severity of congestive heart failure and is an independent predictor of outcome. Finally, BNP changes correlate with variations of hemodynamic profile induced by therapy and can be used for a noninvasive tailoring of treatment. These findings make this peptide a potential "white count" for patients with suspected or confirmed heart failure.