Heart failure (HF) is a common and expensive cardiovascular disease, in economic terms as well as in lives lost. Angiotensin converting enzyme (ACE) inhibitors have been shown to significantly reduce mortality and hospitalisation in HF. However, recent surveys show that the prescription rate of ACE inhibitors for HF is far below what is considered to be optimal. Furthermore, prescribed dosages are usually lower than those recommended based on evidence from clinical trials. This article estimates the consequences, both economic and human, of underprescribing ACE inhibitors in patients with HF. The indication for prescribing an ACE inhibitor varies, and clinical trials have included different categories of patients; it is inappropriate to assess costs in all eligible patients without taking these factors into account. Therefore, we analysed the data with respect to 4 different groups: (i) asymptomatic left ventricular systolic dysfunction (LVSD)--an early stage leading to chronic HF; (ii) chronic HF; and post-myocardial infarction (MI) LVSD differentiated into (iii) post-MI asymptomatic LVSD and (iv) post-MI chronic HF. We also estimated the cost effectiveness of adding an ACE inhibitor to the treatment of patients with HF for whom an ACE inhibitor is not currently prescribed. If only patient populations in which large trials have shown a significant effect of ACE inhibition on mortality are included in the analysis (i.e. excluding asymptomatic patients with LVSD), increasing the number of Swedish patients receiving an ACE inhibitor could save in excess of 3700 lives each year, in addition to reducing the annual number of hospitalisations by 8400. The additional cost would be 101.5 million Swedish kronor (SEK), a cost per life saved of SEK27 200. Chronic HF is the most cost-effective patient population to treat, generating cost savings under certain assumptions. A further 6700 hospitalisations can be avoided should the use of ACE inhibitors be extended to asymptomatic patients with LVSD. Increasing dosages to those used in the large clinical trials may generate additional savings in lives and hospitalisations. In conclusion, the use of ACE inhibitors in HF and LVSD has clearly been proven to be cost effective, and compares favourably with the cost effectiveness of treating hypertension or hypercholesterolaemia. At present, however, ACE inhibitors are not optimally utilised. Given the increasingly constrained resources for healthcare, every effort should be made to increase the use of cost-effective treatments, such as ACE inhibitors in chronic HF and post-MI LVSD.