EnSite NavX-Guided Coronary Sinus Mapping During CRT Implant

Objective(s): To determine the feasibility of CS mapping with NavX during Biventricular Implantable Cardioverter Defibrillator (BiV ICD) implantation. Inclusion Criteria: * Subject is between the age of 18 and 75 years * Subject is willing and able to sign a study specific informed consent * Subject is able to fulfill study requirements * Meet the conventional criteria for implant of a BiV ICD, including; LVEF of ≤35%, QRS ≥ 120 ms and NYHA III-IV * Have persistent CHF symptoms despite contemporary CHF medical therapy * Stable and optimal medical therapy (stability is no changes in past 3 months). * Documented history of ischemic or non-ischemic cardiomyopathy. Exclusion Criteria: * Have any standard device exclusions including tricuspid valve prosthesis/ replacement. * Have a positive urine or serum pregnancy test (if female and of childbearing potential) * Be currently participating in an IDE or IND study.