The heart is located a little behind and below the gills.
The typical fish heart has four chambers. Blood moves through all four in sequence. The circulatory system in fishes is a single circuit, with blood flowing from the heart to the gills and then to the rest of the body.
The flow of blood around the body of a mammal (you included!) is quite different. Blood is pumped from the right side of your heart to your lungs, then flows back to the left side of your heart. From there it is pumped to the rest of your body before returning to the right side of the heart.
Copyright © Australian Museum, 2006