Heart

A hollow organ located slightly to the left of the middle portion of the chest. It is composed of muscle and it is divided by a septum into two sides: the right side which receives de-oxygenated blood from the body and the left side which sends newly oxygenated blood to the body. Each side is composed of two chambers: the atrium (receiving blood) and ventricle (ejecting blood).

Source: NCI Thesaurus (C12727).