The conventional Jarvis-style artificial heart also tries to imitate the functioning of a human heart, with distinct pumps making up a heartbeat. They tend to suffer from mechanical fatigue over time, though, because they have no mechanism for self-repair. There has, however, been some interesting artificial heart research that uses continuous-flow pumps that could conceivably work much better than the current generation of artificial hearts: http://www.popsci.com/science/article/2012-02/no-pulse-how-d...
Dick Cheney has half of one. He has a left-ventricular assist device, which has one pump, but still has a heart that does part of the work. The proposed devices in the PopSci article are two of those pumps together, replacing the heart's functions altogether. These have been implanted into cows and work fine, but haven't worked their way through the FDA yet for non-trial use in people.
