The heart is situated inside the thorax in vertebrates, and in the human body is slightly to the left. The human heart consists of 4 main chambers, 2 atria and 2 ventricles. The right side of the heart receives de-oxygenated blood from other parts of the body and pumps it to the lungs where it is oxygenated and returns to the left side of the heart. The left side of the heart pumps the oxygen-carrying blood to the rest of the body. A heartbeat is a single pumping cycle of the heart which comprises three major stages: atrial systole, ventricular systole and complete cardiac diastole.
The right and left coronary arteries branch off the aorta and then divide into smaller branches, supplying all portions of the heart with blood and oxygen. In order for the heart to function properly, it must receive a continuous supply of fresh oxygen-enriched blood. The coronary arteries surround the heart and carry the blood which nourishes the heart muscle. The right coronary artery supplies blood to the right and back sides of the heart. The left coronary artery divides into two main branches—the circumflex and the left anterior descending—supplying blood to the left side of the heart.
There are four heart valves. They are all one-way valves to keep blood moving through the various chambers of the heart.
The mitral valve guards the opening between the atrium and the ventricle in the left side of the heart. It allows blood to flow forward from the atrium to the ventricle, and prevents blood from flowing backwards. The mitral valve has tiny cords attached to the walls of the ventricles. This helps support the valve’s small flaps or leaflets.
The aortic valve, also called a semi-lunar valve, has three segments that prevent the return of the blood from the aorta to the left ventricle. Valves on the heart’s left side need to withstand much pressure. Sometimes they wear out and leak or become thick and stiff.
The pulmonary valve is located at the junction of the pulmonary artery and the right ventricle. When the right ventricle contracts, the pulmonary valve opens, forcing the blood into the artery which leads to the lungs. It is also a semi-lunar valve. When the chamber relaxes, this valve closes and prevents a backflow of the blood.
The tricuspid valve is located between the upper and lower chamber in the right side of the heart. Its position corresponds to the mitral valve in the left side of the heart.
Abnormal heartbeats, called arrhythmia, or slower or faster heartbeats, called bradycardia and tachycardia, respectively, are dangerous medical conditions which often appear as a result of an underlying condition. One of these is disorders is sudden arrhythmic death syndrome, or SADS. SADS is a condition caused by a hereditary genetic defect which can be triggered by high heart rates (from exercise, for example) or extreme emotional distress. As a result, people with the defect who may be otherwise young and healthy have been known to simply and unexpectedly "drop dead". The condition can be treated with a defibrillator implant, however it is not usually detected until the subject has been observed to have an attack, and such attacks are usually fatal.
A myocardial infarction, more commonly known as a heart attack, occurs when the blood vessels which supply the hearts muscle tissue become partially or totally blocked. Heart attack is the number one cause of death in America.
It is the universal symbol of love and the heart is also called a Valentine.
- http://www.bible.org/page.php?page_id=858.# The seat of Sin, the heart