This is the advantage we human beings have over the other mammals: Their brain and heart are on a single plane, but we stand erect, living in two planes at once.
We have a mind above, looking up to the stars, and from there all things begin. We have a heart below, pumping life into the mind’s vision and drawing it into the real world.
When their roles are lost, mind and heart become a marriage from hell. When they work in harmony, nothing can stand in their way.
Other mammals have brains higher than their hearts. Giraffes, for an extreme example, have their heads higher than their heart by more than the head of a human is higher than the ground.
This is the advantage other mammals have over we human beings: They don't get confused and tricked by those who make up stuff like "their brain and heart are on a single plane".
Dear Anonymous Person,
Another advantage we humans have is the capacity to grasp metaphor and abstraction.
The human being is capable of conceiving an idea, being inspired by that idea, and then taking it into action. We create art, literature, philosophy and science, not out of utilitarian purpose, but simply as an expression of our own inner vision.
So the plane of the mind and heart here is meant in abstractly. The mind is not enslaved to the heart, rather, it is capable of dominating it and taking the lead.