The heart muscle is a little larger than the size of a fist and weighs about 3/4 of a pound. Each day, the average heart beats 100,000 times, pumping over 7,000 liters of blood.
Your heart is located behind and slightly to the left of your breastbone (sternum). The outer layer of the heart is a double-layered membrane called the pericardium through which the blood vessels attach to the heart.
Your heart has 4 chambers
Four types of heart valves regulate heart blood flow:
The heart contracts when the brain sends electrical impulses to the heart, cause the heart to contract. The part of the heart that receives the impulse from the brain is the right atrium. The right atrium contains something called the SA node (heart's natural pacemaker) which receives the impulses and sends the signals further through the muscle fibers of the atria and ventricles, causing them to contract.
The heart rate increases and decreases according to how fast the brain is sending the signals to the SA Node to contract, and whether the heart muscle is able to contract at the pace of the signals.
The heart pumps blood to all the organs, tissues and cells through a complex network of blood vessels, arteries, arterioles, and capillaries. When new blood is pumped into the organs and cells, the blood sent by the heart delivers oxygen and nutrients and removes carbon dioxide and waste products. After the blood delivers new nutrients and picks up the wastes, the blood is sent back to the heart through venules and veins. Your heart and circulatory system make up your cardiovascular system.