MIRACLE EF Clinical Study

Inclusion Criteria: * Patient has diagnosis of chronic heart failure \> 90 days in duration * Has left ventricular ejection fraction (LVEF) between 36% and 50%, inclusive, as documented at baseline or within 30 days prior to enrollment * Is either: (a) NYHA Class III at enrollment or at baseline OR (b) NYHA Class II at enrollment or at baseline, with a documented hospitalization for HF in the 12 months prior to enrollment OR (c) NYHA Class II at enrollment or at baseline, without a documented hospitalization for HF in the prior 12 months, but with BNP ≥250 pg/ml or NT-proBNP ≥1000 pg/ml * Has documented left bundle branch block (LBBB) with QRS ≥130ms at baseline or within 30 days prior to enrollment. * Is in sinus rhythm at time of enrollment or at the baseline visit. * Has had no additions to or subtractions from non-diuretic heart failure medical therapy within 30 days prior to enrollment * Is on maximum tolerated (guideline) dosages of medications in ACC/AHA guidelines for HF, Ischemic Heart Disease, Hypertension and AF as appropriate. * Has signed and dated the study informed consent. * Is able to receive a pectoral CRT-P implant. * Is expected to remain available for follow-up visits. * Is willing and able to comply with the Clinical Investigation Plan. Exclusion Criteria: * Requires permanent cardiac pacing. * Indicated for implantable cardioverter defibrillator (ICD), such as for secondary prevention of prior sudden cardiac arrest, related to prior history of ventricular tachycardia and/or ventricular fibrillation. * Less than 18 years of age, or under a higher minimum age requirement as defined by local law. * Unstable angina or an acute MI within 40 days prior to enrollment. * Coronary artery bypass graft (CABG) or percutaneous coronary intervention (PCI) within the 90 days prior to enrollment. * Chronic (permanent) atrial arrhythmias. Chronic (permanent) atrial arrhythmias are defined as cases of long-standing atrial fibrillation (e.g., greater than 1 year) in which cardioversion has not been indicated or attempted. * Cardioversion for atrial fibrillation within 30 days prior to enrollment. * Treatable pericardial constraint within 30 days prior to enrollment. * Restrictive (infiltrative) cardiomyopathies, such as amyloidosis, sarcoidosis, or hemochromatosis. * Enrolled in a concurrent study, with the exception of a study-manager approved study that is strictly observational in nature and does not confound the results of this study (e.g. registries). * Life expectancy of less than 24 months due to non-cardiac conditions. * Pregnant, or of childbearing potential and not on a reliable form of birth control. * CRT-P, pacemaker, ICD or CRT-D device implanted previously, or currently. * Restrictive, hypertrophic, or reversible cardiomyopathy. * Mechanical right heart valve. * Primary valvular disease and is indicated for valve repair or replacement. * Heart transplant, or is currently on a heart transplant list. * Significant renal dysfunction, as manifested by serum creatinine level \>2.5 mg/dl or ≥275 μmol/L or estimated glomerular filtration rate (GFR) ≤30 mL/min/1.73 m2, which is documented within the 30 days prior to enrollment or at baseline. * Significant hepatic dysfunction, as evidenced by a hepatic function panel (serum) \> 3 times upper limit of normal, which is documented within the 30 days prior to enrollment or at baseline. * Chronic or treatment-resistant severe anemia (hemoglobin \<10.0 g/dL), which is documented within the 30 days prior to enrollment or at baseline. * On intravenous inotropic drug therapy.