The objective of this study is to evaluate the prevalence of sustained ventricular and supraventricular rhythm disorders in patients implanted with a CONTAK RENEWAL TR2 ventricular resynchronization therapy (CRT) device

Inclusion Criteria:

• Moderate or severe chronic heart failure, defined by the presence of NYHA class III or IV symptoms, Intra/interventricular synchronization disorder evaluated by echocardiography and/or Doppler Tissue Imaging (DTI, Yu's method22), Ejection fraction (EF) ≤ 40 %, If previous history of myocardial infarction, MI must be > 60 days from the date of inclusion, Estimated life expectancy > 6 months in the case of concomitant disease, Age ≥ 18 years, Optimal drug treatment of chronic heart failure (according to SFC* recommendations).

Exclusion Criteria:

• Conventional indication for treatment by implantable defibrillator upon inclusion, Cardiac transplant envisaged within 6 months, Unexplained syncope, MI < 60 days before inclusion, Non compliance to drug treatment for chronic heart failure, Any coronary pathology which may be treated by revascularisation.