An earthworm does not have any heart at all. But they do have an organ that acts similar to a heart and is usually called a heart just for simplicity's sake, although it is also called an aortic arch. Earthworms have five of these arches. In between each arch is a gland that helps the worm digest calcium, which it gets from eating a lot of dirt.
The aortic arches (hearts) help pump blood around the body of the earthworm in a similar way to animals that have only one multi-chambered heart. Worm "hearts" don't have chambers. Worms also don't have lungs. They absorb oxygen through their skin and then it gets into their blood vessels. The dorsal blood vessel does a bit of the pumping work, with the hearts helping to keep blood pressure steady
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