what organ is under the heart
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: 1  The right atrium receives blood from the veins and pumps it to the right ventricle. 2  The right ventricle receives blood from the right atrium and pumps it to the lungs, where it is loaded with oxygen. 3  The left atrium receives oxygenated blood from the lungs and pumps it to the left ventricle.