For the ancient Egyptians, the heart (ib) was the source of intelligence, feelings, and actions. A person's memory was also housed in the heart and so at the judgment ceremony (Weighing of the Heart) in the afterlife, the heart was able to speak on behalf of the deceased, accounting to Osiris for a lifetime of deeds. Therefore, heart amulets were used on the mummy to protect the owner's organ and to ensure that his heart gave a positive response at judgment.
 
See last picture as a parallel: https://www.liverpoolmuseums.org.uk/artifact/heart-amulet-24