Acute Evaluation of the Safety of Left Ventricular-left Ventricular (LV-LV) Delays and Its Effects on Mechanical Dyssynchrony

Inclusion Criteria: 1. Have an approved indication for a CRT implant 2. Undergoing or previously received the implant of a St. Jude Medical Promote Q 3221-36 CRT-D with a Quartet Model 1458Q LV lead at participating clinical study site 3. Ability to provide informed consent for study participation and be willing and able to comply with the prescribed evaluations Exclusion Criteria: 1. Have persistent or permanent atrial fibrillation 2. Have an intrinsic heart rate of \<50 beats per minute 3. Have Cheyne-Stokes breathing 4. Have undergone cardiac surgery or coronary revascularization procedure within 3 months prior to enrollment or be scheduled for such procedures 5. Have had a recent CVA or TIA within 3 months prior to enrollment 6. Be less than 18 years of age 7. Be pregnant