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The Heart Primeval (心臓原種 Shinzō Genshu), also known as ZX-31, is the leader of the 31 Machine Primevals, and presumably the most powerful. Created Pasder and Pagliaccio to act as independent "Terminal Programs" - it appears that these two are actually the two halves of Heart itself. As the voice of the Z-Master, Heart spoke using a dual-layered voice consisting of Pasder and Paglaccio's voices in sync - however, once GGG and King J-Der had entered the interior of the Z-Master and fought their way to Heart itself, it instead spoke in a psychotically calm male voice (provided by Kōji Ishii, who also voiced Kotaro Taiga).
Heart possessed the ability to fire powerful yet invisible waves of concussive force (possibly heartbeats, as they could be blocked by Solitary Waves), and was also capable of attacking using "blood vessels" that fired blasts of energy. These weapons were also its weak point, as it was possible to rip open the hollow vessels and thus attack Heart from within.
Destroyed by an explosive release of The Power within the Primeval by King J-Der.