Several clinical trials show that cardiac resynchronization therapy (CRT) in patients with moderate-severe heart failure increases survival, improves quality of life and reduces hospital admissions. The high cost of this new technology, incurred by health organizations at the moment of the implant, requires to assess whether its use is economically rational for the Italian Health Service. The paper summarizes evidences of the impact of CRT on the use of hospital resources and on quality of life, and presents a model to calculate incremental costs per quality adjusted life years (QALYs) gained in patients with moderate-severe heart failure treated with optimal medical therapy. The model is based on efficacy data drawn from clinical trials and on other information concerning the Italian context collected and validated by a team of experts from Assobiomedica and the Italian Federation of Cardiology. The model estimates that the incremental cost per QALY gained attributable to CRT is Euro 63,225 if all effects (years of life gained, increased quality of life and reduction of hospital costs) are censored at the end of the first year after the implant and Euro 21,720 if all effects are censored at the end of the third year. Cost-effectiveness of CRT is thus strongly dependent upon the duration of its effects: longer benefits of the therapy compensate initial costs and thus make the technology more cost-effective. In order to get better estimates of the economic profile of CRT it is required to collect more precise data from routine practice on survival, quality of life and hospital resources. The model presented can be easily adapted to take into account new evidence and to calculate cost per QALY gained in regional and local contexts.