Chronic heart failure is a very prevalent disease in developed countries. In recent decades, very important advances in drug therapy have occurred. However, mortality is still very high. One third of patients with a low ejection fraction and New York Heart Association (NYHA) functional class IIII-IV have a wide QRS. This means that there is often resynchronization of contraction and higher mortality. In order to improve the prognosis, the therapy based on cardiac resynchronization device has bee4n shown to be a complementary medical treatment and has contributed to clinical, hemodynamic and mortality improvements. In this article, we aim to show the results of clinical trials and recommendations of the main guidelines regarding this therapy.