For the acutely ill patient presenting to the emergency department with dyspnea, an incorrect diagnosis could place the patient at risk for both morbidity and mortality. The stimulus for B-type natriuretic peptide (BNP) release is a change in left-ventricular wall stretch and volume overload. A rapid, whole-blood BNP assay (Triage BNP Test, Biosite Inc, San Diego, CA) that allows quick evaluation of the dyspneic patient has recently been approved by the U.S. Food and Drug Administration. Preliminary research with this test set the stage for the recently completed “Breathing Not Properly” BNP Multinational Study, a seven-center, prospective study of 1586 patients who presented to the emergency department with acute dyspnea and had BNP measured with a point-of-care assay upon arrival. BNP was accurate in making the diagnosis of congestive heart failure (CHF), and levels correlated to severity of disease. Knowledge of BNP levels could have reduced clinical indecision by 74%. Algorithms are being developed for use in the emergency department that take into account other illnesses that might raise BNP levels. BNP levels should be extremely important in ruling out and diagnosing decompensated CHF, as long as baseline “euvolemic” BNP values are known. Finally, in addition to helping assess whether a dyspneic patient has heart failure, BNP levels may also be useful in making both triage and management decisions.