heart is considered as the body’s circulatory pump, located in the thoracic cavity. It is made up of four chambers, two upper chambers known as Atria and two lower, thicker walled chambers, known as Ventricles. It has a strong muscular wall and is made up of a special type of muscle known as myocardium, which is only found in the heart. The septum divides the two sides of the heart and four one way valves control the blood flow. The blood flow carries oxygen and vital nutrients to all parts of the body. The blood then returns to the heart via the veins. The blood returns to the heart at the same rate as it is pumped out, it takes just one minute for it to complete a full circuit of the entire body. (Refer to diagram) (Taylor, 1999-2013). [1]
The flow of blood through the heart:
De-oxygenated blood returning from the body enters the superior and inferior vena cava. It enters the right atrium, is pumped through the tricuspid valve into the right ventricle, from the right ventricle it is pumped through the pulmonary semilunar valve to the pulmonary trunk. The pulmonary trunk carries the blood to the lungs, releases carbon dioxide and absorbs oxygen. The blood returns to the heart through pulmonary veins. From the veins, it enters the heart again through the left atrium. The left atrium contracts and pumps blood through the bicuspid valve (mitral) into the left ventricle. The left ventricle pumps blood through the aortic semilunar valve into the aorta. From the aorta blood enters the systemic circulation throughout body tissues until it returns to the heart. Then the cycle begins again. The heart beat sound is known as the ‘lubb’ and ‘dupp’, this is where the blood is pushing on the valves of the heart. The ‘lubb comes first and is longer. The ‘dupp’ is shorter and comes second. This is caused by the opening and closing of the semilunar valves. (Cancer Research, 2013). [1]

The heart wall is made up of three layers: