The human heart weighs between 200 and 425 grams and is a little larger than the size of your fist. By the end of a long life, a person's heart may have beaten (expanded and contracted) more than 3.5 billion times. In fact, each day, the average heart beats 100.000 times, pumping about 6 liters of blood per minute.

It is located between your lungs in the middle of your chest, behind and slightly to the left of your breastbone (sternum). A double-layered membrane called the pericardium surrounds your heart like a sac.

Your heart is a hollow, muscular pump that is divided into 4 chambers. The two top chambers are called atria, and the two lower chambers are called ventricles.

The two atria are separated by an interatrial septum, while the interventricular septum divides the two ventricles. The atrium and ventricle of each side of the heart communicate with each other via an atrioventricular orifice. This orifice can be opened or closed off by an atrioventricular valve (the A-V valve). The left A-V valve is known as the bicuspid (or mitral) valve, while the right A-V valve is termed the tricuspid valve.

The heart is completely divided into a right half and a left half. These two halves act as separate pumps, and there is no mixing of blood between them. Each side is in charge of pumping blood through one of the two blood vessels circulation.

The right heart pumps blood into the pulmonary circuit, while the left heart pumps blood into the systemic circulation. In order to move blood through your heart, your heart chambers undergo alternating periods of relaxation (diastole) and contraction (systole), allowing the chambers to fill up with and pump blood, respectively.

The right atrium of the heart receives deoxygenated blood from two major veins: the superior vena cava and the inferior vena cava, as well as a smaller coronary sinus that drains blood from the heart wall. At the same time newly oxygenated blood enters the left atrium of your heart through your pulmonary veins. Once the atria are filled with blood they contract pushing blood into the ventricles through the bicuspid and tricuspid valves. As soon as they are filled with blood, the two ventricles contract, forcing blood into the aorta and the pulmonary artery.

From the aorta (the main blood supplier to the body), blood travels through the systemic circuit of the blood vessels, bringing oxygen to tissue cells throughout the body. Whether the pulmonary artery brings blood to the lungs to discharge carbon dioxide and enrich itself of oxygen.

The heart muscle, like every other organ or tissue in your body, needs oxygen-rich blood to survive. This blood is supplied to the heart by its own vascular system, called coronary circulation. Two blood vessels, that emerge from the aorta just outside the left ventricle, called the coronary arteries supply oxygen-rich blood to the entire heart muscle.

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