Assess Safety and Probable Benefit of the EXCOR® Pediatric Ventricular Assist Device

Inclusion Criteria: \- Severe New York Heart Association (NYHA) Functional Class IV (or Ross Functional Class IV for patients \<= 6 years) heart failure refractory to optimal medical therapy, and has met at least one of the following criteria: * Interagency Registry for Mechanically Assisted Circulatory Support (INTERMACS) profile status 1 or 1a, i.e. critical cardiogenic shock (low BP unresponsive to support), compromised end organ perfusion, \< 24 hour survival without mechanical support; may be due to Ventricular Tachycardia (VT)/Ventricular Fibrillation (VF) (1A) OR * INTERMACS profile status or 2A (i.e progressive decline): not in imminent danger, but worsening despite optimal inotropic therapy; may be due to VT/VF (2A) AND at least one of the following criteria: Decline in renal functions, Decline in nutritional status, Decline in mobility/ambulation OR * Support with extra-corporeal membrane oxygenation (ECMO) or other mechanical circulatory support device OR * Unable to separate from cardiopulmonary bypass * Listed (UNOS status 1A or equivalent) for cardiac transplantation * Two-ventricle circulation, including cardiomypathy, repaired structural heart disease or acquired heart disease * Age 0 to 16 years * Weight \>= 3 kg and \<= 60 kg * Legal guardian (and patient if age-appropriate) understands the nature of the procedure, is willing to comply with associated follow-up evaluations, and provide written informed consent and assent prior to the procedure Exclusion Criteria: * Support on ECMO for \>= 10 days * Cardiopulmonary resuscitation (CPR) duration \>= 30 minutes within 48 hours of implantation * Body weight \< 3.0 kg or Body Surface Area \> 1.5 m2 * Presence of mechanical aortic valve * Unfavorable or technically-challenging cardiac anatomy including single ventricle lesions, complex heterotaxy, and restrictive cardiomyopathy * Evidence of intrinsic hepatic disease * Evidence of intrinsic renal disease * Evidence of intrinsic pulmonary disease * Hemodialysis or peritoneal dialysis (not including dialysis or continuous veno-venous hemofiltration (CVVH) for fluid removal) * Moderate or severe aortic and/or pulmonic valve insufficiency * Apical Ventricular Septal Defects (VSD) or other compromise that is technically challenging to repair at implant * Documented heparin induced thrombocytopenia (HIT) * Documented coagulopathy * Hematologic disorder * Active Infection within 48 hours of implant (positive blood culture or White Blood Cell Count \>15,000 and fever \> 38 degrees C) * Documented Human immunodeficiency virus (HIV) infection or acquired immunodeficiency syndrome (AIDS) * Evidence of recent life-limiting malignant disease * Stroke within 30 days prior to enrollment * Psychiatric or behavioral disease * Currently participating in another Investigational Device Exemption (IDE) or Investigational New Drug Application (IND) trial * Patient is pregnant or nursing