Congestive heart failure (CHF) is associated with substantial morbidity and mortality, and is the only major cardiovascular disease increasing in prevalence. Despite abundant evidence to support their efficacy and cost-effectiveness, angiotensin-converting enzyme (ACE) inhibitors are sub-optimally used in patients with CHF. This paper reviews the evidence for the sub-optimal use of ACE inhibitors in patients with CHF, the factors contributing to this, and its implications for health systems. A systematic review of all articles assessing practice patterns (specifically the use of ACE inhibitors in CHF) identified by MEDLINE, search of bibliographies, and contact with content experts was undertaken. 37 studies have documented the use of ACE inhibitors in patients with CHF. Studies assessing use among all patients with CHF document 33% to 67% (median 51%) of all patients discharged from hospital and 10% to 36% (median 26%) of community dwelling patients were prescribed ACE inhibitors. Rates of ACE inhibitor use range from 43% to 90% (median of 71%) amongst those discharged from hospital having known systolic dysfunction, and from 67% to 95% (median of 86%) for those monitored in specialty clinics. Moreover, the dosages used in the 'real world' are substantially lower than those proven efficacious in randomised, controlled trials, with evaluations reporting only a minority of patients achieving target doses and/or an overall mean dose achieved to be less than one-half of the target dose. Factors predicting the use and optimal dose administration of ACE inhibitors are identified, and include variables relating to the setting (previous hospitalisation, specialty clinic follow-up), the physician (cardiology specialty versus family practitioner or general internist, board certification), the patient (increased severity of symptoms, male, younger), and the drug (lower frequency of administration). In light of the substantial evidence for reductions in morbidity and mortality, clearly, the prescription of ACE inhibitors is sub-optimal. Wide variability in ACE inhibitor use is noted, with higher rates consistently reported among patients having systolic dysfunction confirmed by an objective assessment--an apparent minority of the those having CHF. Optimisation of the prescription of proven efficacious therapies has the potential to confer a substantial reduction in the total cost of care for patients with CHF by reducing hospitalisations and lengths of hospital stays. It is likely that only multifaceted programs targeted toward the population at large will yield benefits to the healthcare system, given the widespread nature of the sub-optimal prescription of therapies proven effective in the management of patients with CHF.