Binary vascular system

A binary vascular system was a type of circulatory system in which all the blood vessels lead to two hearts. Time Lords were perhaps the most notable species known to possess them (DW: Spearhead from Space, Robot, Doctor Who (1996), The Christmas Invasion).

Others included the near-Human people of the planet Dulkis (DW: The Dominators) and, throughout the galaxy of Mutter's Spiral, a few monopod species, and a drone species (NA: Tragedy Day).

When Henry van Statten performed an invasive scan of the Ninth Doctor, he marveled at the design and enthusiastically announced he was going to patent it (DW: Dalek).