Why must an artificial heart "beat"?!

Why must an artificial heart "beat"?

The biggest problem with mechanical hearts is designing the "beat" mechanism to imitate the organic heart we are born with. I know that "lubdub" sound is really soothing and all, but why can't artificial hearts be made with more effective technology, like a rotary pump?
During transplant operations, they use a rotary (albeit inefficient flexion designed) pump of sorts.
A variable-speed rotary pump would seem to be a lot more efficient. So why can't something like this be used for artificial hearts?

Well, mechanical heart design does not include any mechanism specifically to provide the "lub-dub" sound- it actually is more of a click thump, and it's produced as a byproduct of the pumps action. The heart is after all, a two stage pump- but there are two sides with different pump demands. The atrium fills while the ventrical is emptying, the ventrical fills as the atrium empties into it. And you have two sides, the left supplying the body and the right circulating to the lungs for oxygenation. The pumping action for the right side doesn't have to be as strong as that on the left, as the distance to the lungs is not as great as say that required to get blood to your little toe. And while it is true the heart lung bypass machine uses a rotary pump, it's not trying to pump in two directions at once- it's only coming in and going out in one direction. While it is possible to build a four stage rotary engine, I don't think we are advanced enough to make one of sufficiently small size to do the job. Building artificial hearts that can be transplanted into the human body is not as easy as simply repairing a pump in your car. Even something as simple as the variable speed would not work unless its capable of responding to the neural impulses from the body that normally trigger a faster or slower heartbeat. So far, we haven't been able to build an interface that can do that. And you couldn't afford to have a mess up with the heart rate, so you would still have to maintain some sort of override mechanism just in case there was a malfunction. Now I certainly wouldn't want to stifle invention or inspiration, so I would not say these conditions will always be so. There is always room for innovation, and if you think you can make the ideas work, then I say go for it and try to develop your ideas. Just beware the human body is an intricately designed marvel, and it's complexities are more than we have had much luck imitating or improving on. The heart is one of the simpler organs we own, and yet- still a major callenge to replace.