Most scientific study has focused on ANP and BNP. Measurement of BNP helps doctors diagnose and treat congestive heart failure. In this condition, the heart is unable to pump blood efficiently, and the heart chambers swell with blood. As the heart cells stretch, they produce extra BNP, which pours into the bloodstream. By measuring blood levels of BNP, doctors can spot signs of congestive heart failure in its early stages, when it may be hard to distinguish from other disorders. A normal BNP level is about 98% accurate in ruling out heart failure.