On this particular point, there are slight variations in precisely when you visualize the energy flowing into the heart is indicated. Some techniques specify sending the energy while inhaling to the brain and then the heart, while others specify sending the energy to the heart on the exhalation.

In my view, they are saying the same thing: imagine stirring water in a basin: when your instrument is on the right hand side, the water is still moving on the left hand side. This same movement is happening in pranayama: your attention may be on one spot, but the energy is moving in a circuit, throughout the system.