The Committee for Practice Guidelines (CPG) of the European Society of Cardiology recognizes that new evidence from clinical research trials may impact on current recommendations. The current heart failure (HF) guidelines1 were published in 2008 and the cardiac pacing guidelines in 2007.2 In order to keep these guidelines up to date, it would be appropriate to modify the recommendations and levels of evidence according to the most recent clinical trial evidence. This Focused Update on the use of devices in heart failure 2010 is the first publication of its kind from the CPG. Practice Guideline recommendations should represent evidence-based medicine. Traditionally, these recommendations are based on the outcomes in the cohort of patients described by the inclusion criteria in the protocols of randomized clinical trials (RCTs). More recently, based on the fact that the characteristics of the patients actually included in a trial may differ substantially from the eligibility criteria, Guideline Task Force members frequently favour restricting the applicability of these recommendations to the clinical profile and outcomes of the enrolled cohort, representing a more accurate interpretation of the evidence provided by a trial's result. In contrast to previous guidelines, this focused update considers the characteristics of the patients included in the trials and contains several examples. In MADIT-CRT, although the protocol permitted inclusion of patients in both New York Heart Association (NYHA) I and II function class, only 15% of the patients included in this trial were classified as NYHA I, many of whom had been previously symptomatic. Similarly, although the inclusion criteria permitted randomization of patients with a QRS width of ≥130 m, the favourable effect on the primary endpoint was limited to patients with a QRS width of ≥150 ms, a prospective, pre-specified cut-off. The text accompanying these recommendations explains and justifies the decisions to …