When humans are in the embryonic state of development, we go through a stage called ‘The heart primordial’, when we have two hearts (aka binary vascular system). I mean later on they fuse together into one heart with four chambers, but at one point we’ve all had two hearts. Imagine if your hearts didn’t fuse together and you were left with two hearts!
You’d basically be a time lord.
And on that note, I should end my Doctor Who marathon.