Beginning of Essay
is a specialized, four chambered muscle that maintains blood flow in the circulatory system. The heart is located in the thorax, it lies left of the body's midline, above and in contact with the diaphragm. It is behind the breastbone, or sternum, and between the ....

Middle of Essay
.... ensues shortly. Since heart attacks are the number-one cause of death in the United States, the heart gets a great deal of attention. The heart's wall has three parts, Muscle tissue, or myocardium, is the middle layer. The inner layer, or endocardium, that lines the inside of the heart muscle consists of a thin layer of endothelial tissue overlying a thin layer of vascularized connective tissue. The outside of the heart, the epicardium, is in intimate contact with the pericardium; this serous membrane is a closed sac covering the heart muscles outside wall. Within the sac, a small amount of fluid reduces the friction between the two layers of tissue ....