Objectives: To determine the cost-effectiveness of natriuretic peptide (NP) testing and specialist outreach in patients with acute heart failure (AHF) residing off the cardiology ward. Methods: We used a Markov model to estimate costs and quality-adjusted life-years (QALYs) for patients presenting to hospital with suspected AHF. We examined diagnostic workup with and without the NP test in suspected new cases, and we examined the impact of specialist heart failure outreach in all suspected cases. Inputs for the model were derived from systematic reviews, the UK national heart failure audit, randomized controlled trials, expert consensus from a National Institute for Health and Care Excellence guideline development group, and a national online survey. The main benefit from specialist care (cardiology ward and specialist outreach) was the increased likelihood of discharge on disease-modifying drugs for people with left ventricular systolic dysfunction, which improve mortality and reduce re-admissions due to worsened heart failure (associated with lower utility). Costs included diagnostic investigations, admissions, pharmacological therapy, and follow-up heart failure care. Results: NP testing and specialist outreach are both higher cost, higher QALY, cost-effective strategies (incremental cost-effectiveness ratios of £11,656 and £2,883 per QALY gained, respectively). Combining NP and specialist outreach is the most cost-effective strategy. This result was robust to both univariate deterministic and probabilistic sensitivity analyses. Conclusions: NP testing for the diagnostic workup of new suspected AHF is cost-effective. The use of specialist heart failure outreach for inpatients with AHF residing off the cardiology ward is cost-effective. Both interventions will help improve outcomes for this high-risk group.