The heart of a vampire probably resembles the Life Box of a lich, except that a lich's Life Box seems to be just a coordinate pointing to the real world, while the heart of a vampire is the core of life itself.
Within the long box, Liszt stored away five hearts, including that of Tuobert.
He would not trust vampires.
However, he tossed the clump of blood back to Elizabeth, "Tuobert is dead, unexpectedly. I originally planned to ask him some questions. Now that the pureblood is dead, how do I contact the other four mixed-blood vampires?"
"As long as you squeeze the heart, they will sense it and come to see you. Having the heart, we all become your vampire servants," Elizabeth quickly changed her attitude, showing full gentleness and obedience, after Liszt took possession of the hearts.
It was clear to her that Liszt had become her master.