Heart is a muscular pump, made up of specialized muscles. The right half of the heart receives impure (de-oxygenated) blood from the body and pumps it into the lungs. The left half of the heart receives pure (oxygenated) blood and pumps it to the rest of the body. The left half of the heart is stronger and thicker.
In order to function, the heart needs nourishment. The nourishment comes to the heart via blood which is supplied to the heart through two major coronary arteries : left and right coronary arteries. The left coronary artery again divides into two major branches (left anterior descending and left circumflex arteries), from which several smaller branches arise and supply the heart. Thus, there are three major arteries : left anterior descending artery, left circumflex artery and right coronary artery.