PROSPECT: Predictors of Response to Cardiac Re-Synchronization Therapy

Inclusion Criteria: * Moderate to severe heart failure * Ejection Fraction ( measurement of blood pumped out of the heart) less than 35% * Wide (greater than 130 milliseconds) QRS duration for US patients only. * May include patients with less than 130 millisecond QRS duration if they have mechanical dyssynochrony (uncoordinated heart contractions) in Europe. * All patients enrolled should be stable on medications that include at least an ACE inhibitor or Angiotensin Receptor Blocker (ARB) and at optimal level for at least one month prior to surgery Exclusion Criteria: * Patients that are not eligible for this study are those that have a mechanical right heart valve or are experiencing the following medical conditions within the last 3 months: * Chest pain / unstable angina * Acute heart attack * Chronic or permanent atrial arrhythmias such as atrial fibrillation * Contrary artery bypass graft (CABG) * Percutaneous transluminal coronary angioplasty (PTCA) * Patients who have had intermittent or continuous Inotropic drug therapy are not eligible for this study. * Patients who have had heart transplant or a prior Cardiac Resynchronization Therapy device are not eligible for this study. * Patients who are pregnant or are of child-bearing potential are not on a form of birth control may not participate in this study.