A butterfly's circulatory system is relatively simple. The heart is a pump attached to a long tube that extends from the abdomen to the head. The blood is pumped through this tube and released into the tissues. Through a pressure gradient, the blood seeps through the tissue back to the abdomen. There it is sucked back into the heart and pumped forward again.

In a butterfly, there is no transportation of oxygen in the blood. Butterflies have valves called spiracles along either side of their bodies. Some of these spiracles, located mostly along the abdomen, allow oxygen to enter. Other spiracles exhale carbon dioxide. In this way oxygen will enter the body directly. Once inside, there is a network of tunnels similar to the network of veins in the human body. Oxygen will travel directly to where it is needed and pass into the tissue.