Eve’s Heart (イブの心臓 Ibu no Shinzō?) is a magic circuit installed inside an automaton which gives life to it, allowing it to have autonomous movement, intelligence and its own will, making it its most vital part. It is an extremely flexible magic circuit, as besides being able to give life to an automaton, it can also allow it to reproduce human bodily functions such as breathing, perspiration, and the digestion of food in the hands of a skilled puppeteer; though, it is uncertain how useful these functions are in battle. The Eve’s Heart is the only magic circuit that is an exemption to the Magic Activity Dissonance Theory, being the only particular type of magic circuit compatible to be installed along with another different type of magic circuit within the same body. It is still an unexplained black box as it can only be reproduced, but not reversed engineered or further developed. The Eve’s Heart is easy to generate, becoming excessively popular at presenttime to the extent of every workshop having at least one master skilled at reproducing it, making automata ubiquitous as well. If it is damaged, it can still be repaired, but if it is destroyed, its destruction will lead to the death of an automaton.
The Eve’s Heart's discovery led to the advent of the history of Machinart.