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In humans and most animals, there is a single heart. The heart sustains life by pumping blood throughout the body. However, in nature some organisms have circulatory systems that require more than one heart. There are animals with multiple hearts, and this specialized structure helps them survive in their environments. Organisms Without Hearts Some invertebrates such as jellyfish, corals, sponges, and starfish have no heart. Instead of blood vessels, these organisms have a water vascular system.