The Cardiodefibrilation System[]
The core functionality of the cardio system is a defibrilation unit, implanted to jolt the heart out of arrest. It autonomously measures the pulse of the individual it is implanted into, and should their heart enter into a phase of arrest, the devices attempts to restore the pulse. It is not an artificial heart, but operates in tandem with both natural and artificial hearts.
The device can actually be somewhat dangerous in certain circumstances; for example, an individual with a cardio system must have the system disabled before entering stasis - otherwise, it can cook the heart.
The Secondary Heart Augmentation[]
The secondary heart normally operates as a secondary pump, operating in tandem with and assisting the bearer's primary heart. The true function of the secondary heart comes into place if the primary heart enters arrest: It seamlessly takes over as primary pump while the defibrilation unit attempts to restore primary heart functionality.
This is often accompanied by a surge of adrenaline and a noteworthy state of panic, including normal sensations of parasthenia and a fight or flight response. The secondary heart possesses its own defibrilation unit, as well.