Prospective, multi-center, single arm, post approval study to be conducted in the United States.

Evaluate the effectiveness of Boston Scientific (BSC)'s LV MSP (Left Ventricular MultiSite Pacing) feature in the Resonate family of CRT-D devices and confirm safety in a post approval study when used in accordance with its approved labeling.

Inclusion Criteria:

1. Subjects who received de novo implantation of BSC's Resonate family of CRT-D devices with the LV MSP feature4 and BSC's ACUITYTM X4 LV Quadripolar leads. A Resonate family of CRT-D device upgrade from previous single or dual chamber pacemaker or ICD implantation is allowed.
2. Subjects must meet BSC labeled indication for CRT-D implantation.
3. Subjects must have a functional RA lead and RV lead implanted
4. Subjects who are willing and capable of providing informed consent
5. Subjects who are willing and capable of participating in all testing/visits associated with this clinical study at an approved clinical study center and at the intervals defined by this protocol
6. Subjects who are age 18 and above, or of legal age to give informed consent specific to state and national law

Exclusion Criteria:

1. Subjects who received LV pacing prior to receiving the Resonate family of CRT-D system implantation.
2. Subjects who received the LV MSP therapy post CRT-D implantation but prior to enrollment
3. Subjects with documented history of permanent AF
4. Subjects with documented permanent complete AV block
5. Subjects who are expected to receive a heart transplant during the 12 months course of the study
6. Subjects with documented life expectancy of less than 12 months
7. Subjects who enrolled in any other concurrent study or registry, with the exception of mandatory national or governmental registry, without prior written approval from BSC