Step 1 : Introduction to the question "Which creature has three hearts?"
...Octopuses are the bizarre cephalopods who are extremely smart and very good at squeezing through tight spaces. But that isn't the only thing that makes them remarkable. Octopuses have three hearts. One heart keeps the blood flowing through the circulatory system to the body's organs. The other two hearts work to move blood beyond the octopus's gills. When an octopus swims, the organ heart will stop beating. This explains why the octopus prefers to crawl rather than swim - an activity they find exhausting. Source: SmithsonianMag.com