The heart is a muscular organ about the size of a fist, located
just behind and slightly left of the breastbone. The heart pumps
blood through the network of arteries and veins called the
cardiovascular system. The heart has four chambers: - The right
atrium receives blood from the veins and pumps it to the right
ventricle. - The right ventricle receives blood from the right
atrium and pumps it to the lungs, where it is loaded with
oxygen. - The left atrium receives oxygenated blood from the
lungs and pumps it to the left ventricle. - The left ventricle
(the strongest chamber) pumps oxygen-rich blood to the rest of
the body. The left ventricle’s vigorous contractions create our
blood pressure. The coronary arteries run along the surface of
the heart and provide oxygen-rich blood to the heart muscle. A
web of nerve tissue also runs through the heart, conducting the
complex signals that govern contraction and relaxation.
Surrounding the heart is a sac called the pericardium.