Acute Feedback on Left ventrIcular Lead Implantation Location for Cardiac Resynchronization Therapy

Inclusion Criteria: * Subject is indicated for CRT or CRT-D device according to current applicable ESC/AHA guidelines * Subject is in stable sinus rhythm at the time of implant (no atrial arrhythmias lasting \> 30 seconds during the last 2 weeks prior to inclusion). No documented AF-episodes allowed during the last 2 weeks prior to inclusion. * Subject receives optimal heart failure oral medical therapy (ACE inhibitor and/or ARB and Beta Blockers), and is on a stable medication scheme for at least 2 months prior to enrollment. * Subject (or the legal guardian) is willing to sign informed consent form Exclusion Criteria: * Permanent atrial fibrillation/ flutter or tachycardia * RBBB * Recent myocardial infarction (MI), within 40 days prior to enrollment. Subject underwent coronary artery bypass graft (CABG) or valve surgery, within 90 days prior to enrollment * Post heart transplantation, or is actively listed on the transplantation list, or has reasonable probability (per investigator's discretion) of undergoing transplantation in the next year * Implanted with a left ventricular assist device (LVAD), or has reasonable probability (per investigator's discretion) of receiving a LVAD in the next year * On chronic renal dialysis, or with severe renal disease (defined as estimated Glomerular Filtration Rate (equation provided by Modification of Diet in Renal Disease study): (eGFR) \< 30 mL/min/1.73m2) * On continuous or uninterrupted infusion (inotropic) therapy for heart failure (≥ 2 stable infusions a week) * Severe aortic stenosis (with a valve area of \<1.0 cm2 or significant valve disease expected to be operated on within study period) * Complex and uncorrected congenital heart disease * Mechanical heart valve * Breastfeeding women, or women of child bearing potential and who are not on a reliable form of birth control * Enrolled in one or more concurrent studies that would confound the results of this study * Already implanted with pacemaker (CRT, CRT-D, ICD) and needs replacement