Contractile Reserve in Dyssynchrony: A Novel Principle to Identify Candidates for Cardiac Resynchronization Therapy

Inclusion Criteria: * Subject is indicated for CRT device according to European Society of Cardiology (ESC) guidelines from 2013. * Subject is willing to sign informed consent form and is 18 years or older. Exclusion Criteria: * Right bundle branch block. * Recent myocardial infarction, within 40 days prior to enrollment. * Subject underwent coronary artery bypass graft (CABG) or valve surgery, within 90 days. * 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 LV assist device (LVAD), or has reasonable probability (per investigator's discretion) of receiving a LVAD in the next year * 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. * Breastfeeding women or women of child bearing potential. * Enrolled in one or more concurrent studies that would confound the results of this study. * Impossible to obtain LV volumes by echocardiography