Being a Gallifreyan, Doctor Who has a binary vascular system, where the blood vessels lead to two hearts. If the Time Lord can function with two hearts, can humans do the same?
Aside from conjoined twins, no human is born with two hearts. But in the case of extreme heart disease, called cardiomyopathy, rather than receiving a donor heart and removing yours, doctors can graft a new heart on to your own to help share the work. This is more commonly known as a piggy-back heart.
Some animals like the octopus have more than one heart. An octopus has one main, systemic heart that pumps blood to the whole of its body. But it also has two additional hearts, responsible for pumping blood over each of its gills.
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