But to imagine the heart mechanically, as a pump, is to forget the central conundrum: How do you make a pump out of cells? A pump is, after all, a highly coordinated machine. It needs a signal to dilate and a signal to compress. It needs valves to ensure that the fluid doesn’t flow backward. It requires a mechanism to ensure that the contracting bladder doesn’t wobble without purpose or direction. An uncoordinated pump is no better than a wobbling balloon.
