The thesis evaluated the role of the B-type natriuretic peptides and N-terminal pro-B-type natriuretic peptides in the management of heart failure patients. In a population-based retrospective cohort study of electronic medical records, the thesis examined the patterns of natriuretic peptide testing in primary care practices within the United Kingdom. The thesis showed that single brain natriuretic peptides and N-terminal pro brain natriuretic peptides were independent predictors of all-cause mortality and cardiovascular mortality in the primary care setting. In a small subgroup of patients with two natriuretic peptides measured, changes in brain natriuretic peptides did not provide additional prognostic information beyond a single point-in-time peptide level. Age adversely impacted the mortality especially in elderly. In a clinical trial setting, the thesis also investigated the within-subject variability of B-type natriuretic peptides, vital signs and serum creatinine over a three-month period in stable chronic heart failure patients with New York Heart Association class II-III. Correlations between B-type natriuretic peptides and cardiac structure factors, weight, heart rate, blood pressure and serum creatinine were estimated. The B-type natriuretic peptide within-subject variability was 46%, much higher than the heart rate or blood pressure within-subject variability of 10%, serum creatinine within-subject variability of approximately 8% and weight within-subject variability of 1%. The three-month monitoring interval of B-type natriuretic peptides in stable chronic heart failure was too short. Extended monitoring intervals should be further investigated. Monitoring natriuretic peptides in primary care provides an opportunity to positively impact the burden of heart failure by better directing management for patients with poorer prognoses and better utilizing health care resources.