The heart is the muscular organ situated in between the lungs, behind the sternum and slightly tilted towards the left side of the breastbone. Rhythmic muscular contractions activate the heart to pump blood through a system of arteries and veins called the cardiovascular system.
The blood that goes into the right atrium of the heart from the veins, is pumped into the right ventricle. Blood is subsequently pumped to the lungs, to obtain oxygen. The pure oxygenated blood is pumped back from the lungs to the left atrium of the heart. The left ventricle, receives pure blood from the left atrium and pumps it to all the body tissues.