Heart Crush is an extremely high level spell, that works by causing the blood cells in a person's heart (and if you're particularly skilled their entire body) to move inward, attempted to crush the heart like a soda can. It works by pitting the will of the caster against the will of the victim. If the victim wins, then yay! No heart crushed. If the mage wins, then the victim's heart is crushed, effectively dooming them to die. This spell requires the utmost concentration to accomplish, and is only available to masters of Blood Magic.