Heart of sea squirts alternates the direction in which it pumps Blood.

http://en.wikipedia.org/wiki/Ascidiacea

Unusually, the heart of sea squirts alternates the direction in which it pumps blood every three to four minutes. There are two excitatory areas, one at each end of the heart, with first one being dominant, to push the blood through the ventral vessel, and then the other, pushing it dorsally.