Surprised They Aren't Around Yet

Artificial hearts. Don't we already have the mechanical and control technology to create something to keep pumping continuously? Once in a while, the patient removes the used battery and puts in a new one - he always has two in his artifical heart - and both the charger and the heart will ensure the battery is okay. Acutally, the battery could be a smart battery that can decide for itself (has enough functionality embedded in it) if it is ready for the job or not.