The heart is a hollow muscular organ. It is located between the lungs approximately in the middle of the chest. It is positioned in the thoracic cavity between the sternum and the vertebrae. It was placed there meticulously so that it can be compressed or squeezed in case of emergency. The heart is protected in the front by the ribs and in the back by the vertebrae. The average adult's heart is about the same size or a little bigger than their fist weighing about nine to eleven ounces. A newborn baby's heart weighs about two-thirds an ounce.
             Three layers of tissue make up the heart. A membrane called the pericardium is the covering of the heart it surrounds the epicardium. The epicardium is the outer layer of the skin and is made up of epithelial tissue. The next layer is the myocardium, this is the layer that is made up of cardiac muscle. It is also the thickest layer of tissue in the heart. The inner layer of the heart is called the endocardium. This covers lines of the chambers inside. The inside of the heart consists of four major chambers. The wall that separates the chambers is called the septum. Two lower chambers are called ventricles and two upper chambers are called atria. The ventricles are usually larger than the atria. The blood exits through the ventricles and is mostly known as the discharging chambers. The atria are a lot smaller and thinner. They are usually known as the receiving chambers because the blood enters through the atria.
             The heart has four valves. The function of each valve is to prevent backflow. Between the atrium and the ventricles, there are valves called atrioventricular valves. The two valves located between the left atrium and ventricle are called the bicuspid valve. The two valves situated between the right atrium and ventricle are called the tricuspid valve. The bicuspid and tricuspid valves are there to make sure no blood gets through when the ventricles contract. The other two valves are t...