OBJECTIVES:  Heart failure (HF) is a major and growing public health problem associated with high risks of hospitalisation and mortality. B-type natriuretic peptide (BNP) is used as a monitoring strategy to guide treatment of some patients with HF with a reduced ejection fraction (HFrEF) or preserved ejection fraction (HFpEF). However, many clinical guidelines do not recommend routine monitoring, and it is unclear whether the benefits of BNP-guided monitoring outweigh the costs. We assessed the cost-effectiveness of BNP-guided monitoring in various patient subgroups. METHODS:  We used a Markov model with 3-month cycle length to evaluate the cost-effectiveness of BNP-guided monitoring strategy against clinically-guided monitoring strategy in recently hospitalised patients with HF. We estimated the lifetime costs and health benefits (quality-adjusted life-years; QALYs) of a hypothetical cohort of 1,000 patients from a UK National Health Service perspective. We ran the model for five subgroups: all-HF-patients <75yrs (years); all-HF-patients ≥75yrs; HFrEF-patients <75yrs; HFpEF-patients <75yrs; and HFrEF-patients ≥75yrs. We used individual patient data meta-analyses and linked primary care, hospital and mortality data to inform the key model parameters. We performed probabilistic sensitivity analysis to assess the uncertainty in model parameters. RESULTS:  At the willingness-to-pay threshold of £20,000 per QALY, the incremental net monetary benefits for BNP-guided strategy were: £6,426 (95% percentile CI: £2,401 – £10,075) for all-HF-patients <75yrs; £869 (-£2,814 – £4,606) for all-HF-patients ≥75yrs; £5,424 (£987 – £9,469) for HFrEF-patients <75yrs; £3,155 (-£10,307 – £11,613) for HFpEF-patients <75yrs; and £2,267 (-£1,524 – £6,074) for HFrEF-patients ≥75yrs. The probabilities that BNP-guided strategy is cost-effective were: 0.99 (all-HF-patients <75yrs); 0.67 (all-HF-patients ≥75yrs); 0.99 (HFrEF-patients <75yrs); 0.75 (HFpEF-patients <75yrs); and 0.88 (HFrEF-patients ≥75yrs). CONCLUSIONS:  We found strong evidence that BNP-guided monitoring is a cost-effective alternative to clinically-guided monitoring in younger patients (<75yrs) with HFrEF. It is potentially cost-effective in younger patients with HFpEF and older patients (≥75yrs) with HFrEF, however more evidence is required.