For one thing there’s no pulse. The human body is very much designed assuming one.
The Abiocor, first implanted in July 2, 2001, does have a pulse.
But just for one… your arteries contain one-way valves and smaller pumps, to keep blood from pooling in your legs, or from failing to reach your head. These aren’t absolutely critical—children don’t die while standing on their heads—but I can’t imagine they’ll work quite as intended without pulses.
You can’t just swap the main pump on a massive hydraulic system for a different design, and not expect something to go wrong.