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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 cardiac muscle is the heart, responsible for pumping blood throughout the body. It is made up of cardiac muscle and is the only place in the body where such muscle is found. All the other muscles in the body are composed of either skeletal muscle or smooth muscle. The most muscular part of the heart is its middle layer, called the myocardium, which is mainly responsible for its contractions.