Dr Joe Dispenza speaking about heart and brain coherence suggests that it has a lot to do with our brainwave state.
Our brains are either in:
or the ever elusive Gamma.
The ideal is to be in the alpha brainwave because that is where we can be creative, calm, and come up with solutions.
In this video interview, Dr. Joe Dispenza speaks about the differences of these brainwaves and how to go about having heart coherence by having the brain in sync with the body.
Also, to learn more about brainwave states, you might like this review of Dr Joe's book which has a chapter about the various brainwave states and how they function.