Cardiac resynchronization therapy (CRT) is a device implanted to improve the function of some people's hearts. CRT involves the placement of 3 wires in the heart through a vein near the front of your left or right shoulder into three pumping chambers of the heart, the most important being the left lower chamber, left ventricle (LV).

The purpose of Cardiac resynchronization therapy (CRT) is to send small amounts of energy (called pacing) through the wires to both the left and right lower chambers of your heart at (or near) the same time. This helps the heart pump in a more coordinated way and send more blood to your body with each beat. How much energy is used for pacing is called the stimulus intensity. Increasing the pacing stimulus intensity of the left ventricular wire can lead to an increase in the volume of heart muscle directly stimulated. This has previously been shown to produce beneficial effects on the heart function, like strength of contraction and increased volume of blood pumped. The purpose of this study is to determine if pacing the wires in the left ventricular chamber of the heart using higher stimulus intensity improves the strength of the heart's contraction.

Inclusion Criteria:

• Adults who fulfill approved criteria to receive a cardiac resynchronization device.

Exclusion Criteria:

-Adults who are unable to give informed consent.