The heart is the hardest muscular organ of the human body as it works non-stop pumping around 2000 gallons of blood throughout the body everyday through the network of arteries and veins.The heart is a muscular pump not bigger than a large fist and weighing 8 to 12 ounces located between the lungs in the middle of the chest slightly to the left of the center. Each day, the average human heart beats about 100,000 times and as the heart contracts it pumps blood which delivers oxygen and nutrients to every cell and carries deoxygenated blood to the lungs with the carbon dioxide and other waste products made by those cells.
The heart has four chambers; two chambers at the top of the heart are known as the atria/artrium, the two bottom chambers are the ventricles. The atria/artrium receive deoxygenated blood that returns from the different parts of the body, while the ventricles pump the oxygen rich blood back to all body tissues. It is also made up of four valves: the tricuspid, pulmonary, mitral and aortic valves.Valves that separate the atria/artrium from the ventricles are called the atrioventricular valves which are two - the tricuspid on the right and the mitral on the left. Two Valves at the ventricular outlets are called semilunar valves named as the pulmonary and the aortic valves.
The right ventricle pumps the blood through the pulmonary valve to the lungs, where it is made oxygen-rich.The left atrium receives oxygenated blood from the lungs and pumps it through the mitral valve to the left ventricle. The left ventricle pumps oxygenated blood through the aortic valve to the aorta and the rest of the body.The aorta is the largest artery in the body. Blood full of oxygen is pumped by the left ventricle into the aorta. Like all other muscles of body, the heart also needs oxygen to work which is brought to the heart by the coronary arteries.
The heart wall consists of three layers: the external layer is epicardium, the middle layer is myocardium, and the inner layer is endocardium. The epicardium and endocardium are thin layers out of which the endocardium is a thin layer of endothelium. The myocardium forms the main bulk of the heart and is made up of cardiac muscle fibers. The outermost layer/sac that surrounds the entire heart is called the pericardium. Vessels that carry blood away from the heart to the body are called arteries, while those that bring it back are called veins.
The heart also has an electrical system made up of nodes and conducting fibers that generates and transmits cardiac impulse that causes the heart to beat . A complex web of nerve tissues also works through the heart, conducting the complex signals that govern contraction and relaxation.