B-type natriuretic peptide (BNP) and N-terminal proBNP (NT-proBNP) are promising markers for heart failure diagnosis, prognosis, and treatment. This systematic review addresses these four main questions: 1. What are the determinants of both BNP and NT-proBNP measurement? 2. With respect to the diagnosis of heart failure: a. What are the clinical performance characteristics of both BNP and NT-proBNP measurement in patients with symptoms suggestive of heart failure (HF) or with known HF i. presenting to the emergency department (ED) ii. in a specialized clinic or outpatient setting iii. presenting to a primary care setting iv. presenting in long term care setting v. all settings combined b. Does measurement of BNP or NT-proBNP add independent diagnostic information to the traditional diagnostic measures of HF in patients with symptoms suggestive of HF? 3. Do BNP or NT-proBNP levels predict cardiac events in populations: a. Specific populations i. at risk for coronary artery disease (CAD) ii. with diagnosed CAD iii. with diagnosed HF b. What are the screening characteristics of BNP or NT-proBNP in general asymptomatic populations? 4. Can BNP or NT-proBNP measurement be used to monitor response to therapy?