> size of the heart

Size of one heart has restrictions that are determined by diminishing return of physics. That doesn't mean engineering a larger system is impossible or even that very difficult. Same as any other pump system. i.e. there is no reason not to have 2 or 10 hearts.

We do this to move any fluid like water or concrete up to steep terrain or maintain pressure in everything from sewage to oil or gas pipes over long enough distribution systems.

Romanticizing in popular culture not withstanding, heart is just a pump[2] and today can be replaced by (albeit for short duration) entirely by a machine or replaced in a transplant.

We are not talking about say the brain or the central nervous systems[1]. That would be like going to multi-master from single node - lot more fundamental complex rebuild and rethink of the core architecture.

[1]We are not even remotely close to fully understanding let alone attempting to replace.

[2 Amazingly well designed, very efficient, something today we probably could not (yet) build synthetically with similar reliability and durability but it is still a pump nonetheless.