The heart is the main organ of the cardiovascular system. Its job is to pump blood to all parts of the body through a network of vascular channels knowns as veins and arteries. The heart pushes out oxygenated blood through the arteries to be carried to all parts of the body. The oxygen-deprived blood is carried back to the heart through the venous system.
Approximately 7200 liters of blood is circulated through this system each and every day at a rate of 5 liters per minute. Should the heart fail, the rest of the bodily organs, including the brain, would be deprived of oxygen. Within minutes, they too would fail and the person would die. A fully grown heart is about the size of an adult fist - small, to say the least, for having such great responsibilities!
The heart sits within the pericardial cavity between the right and left lungs and is enclosed by a layer of skin called the pericardial sac. It is composed of four main chambers, the right/left atria and the right/left ventricles. The right atrium is like a Grand Central Station for blood vessels that run into the heart. Three main oracles in the heart's right atrium admit the veins from all over the body, except from the pulmonary system, that carry oxygen-deprived blood back to the heart for re-oxygenation. These oracles are known as the superior vena cava, the inferior vena cava and the coronary sinus. The pulmonary veins all meet in the four chambers of the heart's left atrium.
Once in the heart, blood binds with oxygen and is sent back out to all parts of the body, including the brain, through the arterial pathway. The blood is pushed along its path by the contraction of the heart muscles. Both atria contract simultaneously to admit the incoming blood. Within the regions of the heart, the blood is supplied with oxygen and passed out into the body when both right and left ventricles simultaneously contract.
The heart is made up of muscle tissue whose contractions work in a pump-like fashion to push blood through the veins and arteries that carry oxygenated blood to all parts of the body and deoxygenated blood from all body parts back to the heart to start the cycle all over again - all in a matter of seconds. When we listen to the heart through a stethoscope, we hear the contractions of the heart as it beats out the rhythm of life.