Specifically, would there be room within a proportionate humanoid body for a complete duplicate of the circulatory system to grow from birth?
Assume:
That each branch of this circulatory system needs to distribute whatever's in it to the same bodily tissues that the main circulatory system does.
That these two circulatory systems pump different fluids, and do not overlap.
That there's a heart-sized organ at the core of this secondary circulatory system, which is responsible for providing pumping pressure.
That the genes for this exist, meaning that the body is capable of building this thing.
That said heart-sized organ can be anywhere within the body that isn't already occupied by another bodily structure - in other words, no re-arranging organs inside this thing.
That said heart-sized organ does not need to be within proximity to the lungs.
Note that I'm not asking about what evolutionary pressures would lead to such a thing existing, nor am I asking about what a secondary circulatory system could be used for, nor am I asking about what genes would be necessary for this to happen; I'm simply asking whether there's enough physical volume within the humana humanoid body plan to do so.