The heart is an amazing powerful muscle which is a hollow upside down pear shaped shell, which consists of cardiac muscle fibres that contract and cause a wringing type of action. Located just to the left of the centre of the chest its size is a little larger than the size of your fist. The wall of the heart consists of three layers.
Epicardium, Myocardium and Endocardium
The epicardium is the thin outer layer that gives the heart the smooth slippery texture. The endocardium is the smooth inner lining with large blood vessels and the myocardium makes up the bulk of the heart. It is made up of strong cardiac muscle fibres and is in control of the pumping action.
The heart has two sides the right side being the one that pumps the deoxygenated blood to the lungs via the pulmonary artery and the left receives blood oxygenated by the lungs through the pulmonary vein. This forms a double circulation as the oxygenated blood gets pumped to the body in the aorta which then eventually returns back to the right hand side in the vena cava which enables this process to start all over again.
This double circulation which involves the contracting of the heart is called the cardiac cycle. This has two major phases the diastole and the systole. Diastole is the period between ventricular contractions where the right and left ventricles relax and fill. The systole phase occurs when the ventricles of the heart contract, this results in a high pressure within the systemic and pulmonary circulatory systems. These coordinated series of events takes place simultaneously on both the right pulmonary circuit and the left systemic circuit of the heart.
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