User blog comment:Lord Loss/Monster Appreciation Week: Dire Miralis/@comment-6050823-20131012004307/@comment-17735225-20131014101948

The heart might not actually be immortal. As someone pointed out in Theory blog, which makes a lot of sense. Dire Miralis probably use energy from mineral deposit it gathered from water/ore it possibly devour, and circulate throughout its body to process and produce heat and energy for it. Because its 'blood' is almost comparable to magma in density, the heart that pump must have really powerful force to constantly circulate the liquid all over its huge body, most efficient way is to keep the energy up and keep the frequency of beating down. Normal chemical reaction supported with some energy seems to be the best choice here.

The glowing parts on its body are probably the place where most of the waste in its blood precipitated and solidified before being unleashed into the air as meteors. They might also be the place the energy procedure occurs (think of them like mini factories within a volcano).

The heart is probably made to be able to store vast amount of energy in case it cooled itself down too much(prolonged fight in the water) or some creature managed to damage its chest, or in the most important case; hibernation. So when the dragon dies, the ongoing chemical reaction and vast amount of energy remaining (due to not having to pump anything). Made the heart looks like it's still beating, and can still going for a very long time.