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Above is a diagram of an open circulatory system. An open circulatory system is made up of a heart, vessels, and hemolymph. This diagram shows how the hemolymph, fluid present in most invertebrates that is equivalent to blood, is circulated throughout the body of a grasshopper.
The wall of the heart is made up of three layers: epicardium, myocardium, and endocardium. The heart is a muscular organ that pumps blood throughout the body, with a rhythm determined by a group of pacemaking cells in the sinoatrial node. These generate a current that causes contraction of the heart, traveling through the atrioventricular node and along the conduction system of the heart.