The purpose of this study is to evaluate the safety and performance of the MediGuide™ system during CRT implants.

Inclusion Criteria:

• Meet clinical indication for implantation of an SJM CRT system according to the current European Society of Cardiology (ESC) Guidelines for cardiac and resynchronization therapy
• Receiving a new implant or undergoing an upgrade from an existing ICD or pacemaker implant with no prior LV lead placement
• Ability to provide informed consent for study participation and are willing and able to comply with the prescribed follow-up tests and schedule of evaluations

Exclusion Criteria:

• Currently participating in any other clinical study
• Have prosthetic valves
• Are pregnant or planning pregnancy in the next 1 month
• Are less than 18 years of age
• Have ventricular tachyarrhythmias resulting from transient or correctable factors such as drug toxicity, electrolyte imbalance, or acute myocardial infarction