This has come up here before. Muscle, regardless of the animal, needs Oxygen to function. The distance a Deer can travel with a heart shot is directly related to how much blood it is pumping effectively. As long as a sufficent amount of blood is being oxygenated and circulated the Deers muscle, it can function. I have been amazed at how far Bow hit heart shot Deer have travel. I"ve seen them go over two hundred yards and almost four hundred. I realize that is rare but it does happen.
I had a friend hit a Deer in the leg and cut the main artery there and the Deer go only 20 yards and drop. Bleed out, no oxygen to the muscle.