IIRC, the problem with conventional mechanical pumps is that they're continuous-flow. Various other systems in the human body rely in the ebb-and-flow of a pump

IIRC, the problem with conventional mechanical pumps is that they're continuous-flow. Various other systems in the human body rely in the ebb-and-flow of a pumping heart to function correctly, and different activities require different flow speeds. Yes, we can probably engineer a variflow pump as well, and maybe also one that increases and decreases its flow based on hormonal signaling, but it's not as simple as taking your average aquarium pump and connecting it in-place. AFAIK, we have no idea how the heart determines its flow rate.