The EnSite Real-Time Cardiac Performance Measurements Study (EnSite RT CPM) is a multicenter, international, acute, non-significant risk study, designed to enroll a maximum of 40 patient. The goal of the study is to collect 3-D systolic/diastolic data with the EnSite NavX Mapping system during a CRT implant.

Patients enrolled in this study will undergo NavX CPM recording of the heart using the EnSite NavX Mapping system during the implantation of a cardiac resynchronization therapy device.

Inclusion Criteria:

• Be undergoing a new St. Jude Medical CRT-D or CRT-P device implantation
• Have the ability to provide informed consent for study participation and be willing to comply with the prescribed perioperative evaluations

Exclusion Criteria:

• Have a recent myocardial infarction within 40 days prior to enrollment
• Have undergone cardiac surgery or coronary revascularization procedure within 3 months prior to enrollment or be scheduled for such procedures
• Be less than 18 years of age
• Be pregnant women
• Be currently participating in a clinical study that includes an active treatment arm

Patients indicated for implantation of a CRT pulse generator