QRS complex (≥ 120 ms) who also suffer from left bundle branch block (LBBB), or for patients without left bundle branch block but who have a preserved sinus rhythm and a QRS complex with a width of ≥ 150 ms. However, only 30-40% of all heart failure patients show such a prolonged QRS complex, and therefore the 60-70% of patients who have a normal QRS complex cannot be treated with CRT. In addition, around 30% of the patients eligible for CRT treatment do not respond to CRT. Until recently, the only other available device-based treatment was the left ventricular assist device (LVAD). LVAD therapy is indicated in patients with severe illness and is associated with several hours of surgery (involving a cardiopulmonary bypass). It is usually considered as a therapy providing a "bridge to transplant" for heart failure patients classified as NYHA class IV, and is intended to support heart function until a heart transplant is received. Current research results suggest that the therapeutic gap described above could now be closed by the cardiac contractility modulation therapy. Additionally, a long-term study showed that the cardiac contractility modulation was able to stop the common and prognostically unfavorable long-term prolongation of QRS duration in heart failure patients. This result was interpreted as signaling the safety of the treatment and as an indicator that patients could benefit from cardiac contractility modulation therapy in the long term. If the QRS-stabilizing effect were to be confirmed in further studies, the cardiac contractility modulation would become the first device-based treatment for heart failure with the potential to halt QRS prolongation, a factor associated with a poor prognosis. Recommendations The guidelines issued by the European Society of Cardiology (ESC) in 2016, mention cardiac contractility modulation therapy as a therapy option to be considered in selected group of patients with HF. Mostly these guidelines are endorsed by national cardiac societies in individual countries within the European Union. Efficacy Cardiac contractility modulation has proven to be effective and safe in randomized controlled trials involving several hundred patients. The nature and extent of the effect of cardiac contractility modulation have been the subject of numerous investigations. Although various individual publications, as well as one of two meta-analyses, have presented the efficacy and significant potential of cardiac contractility modulation in the treatment of heart failure, medical evaluation of the therapy efficacy is not yet complete. Scientists point out, however, that this