The human heart is a biological pump located in the chest cavity that circulates blood through the cardiovascular system. It is composed of four chambers - two upper atria and two lower ventricles separated by partitions to prevent mixing of oxygenated and deoxygenated blood. The right atrium receives blood from veins and pumps it to the right ventricle to be sent to the lungs, while the left atrium receives oxygenated blood from the lungs and pumps it to the left ventricle to be circulated through the body. The heart is surrounded by membranes called pericardium for protection and support.