The Rockbreaker Heart is a vital component harvested from the massive, burrowing machines known as Rockbreakers in Horizon Zero Dawn. This organ is roughly the size of a human torso, with a robust, cylindrical shape that tapers slightly at one end, resembling a large, mechanical heart. Its surface is a combination of smooth, metallic plates and exposed, fibrous cabling that pulses with a faint blue glow, indicating its energy-rich nature. The exterior is weathered and scratched from the machine's subterranean lifestyle, with patches of rust and dirt embedded in the crevices. The heart's core emits a soft hum and occasional sparks, suggesting its unstable power source.