Exploratory, prospective, interventional, non-randomized single-center research study to compare metrics derived from 2 or 3-D reconstructions of lead movement, bioimpedance and VCG to augmentation of left ventricular contractility (LV dP/dt max) at different pacing configurations in patients undergoing a CRT-implant. Pacing sites and contractility data will be compared to pre operative cardiac ultrasound and MRI metrics.

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