It is the process of hardening of arteries which are elastic and flexible at early age. It happens with all the arteries of body but may be critical for heart or brain. The process starts with deposition of fat particles (Fatty streak) in the inner wall of artery. Progressively there is accumulation of white blood cells, smooth muscle cells and cellular debris forming a lump (Plaque or atheroma). This plaque protrudes in the lumen and reduces the blood supply. This process of atheroma formation takes years but can develop early and if the level of fat in body is high (especially LDL cholesterol) or there is presence of other factors which favors the atheroma formation. This process of atherosclerosis occurs throughout the body but at different pace so that it can cause significant obstruction in any one of the arteries. Furthermore if the process of atherosclerosis is slow, collateral vessels develop to supply the area of scarcity, reducing the chances of severe damage. In CHD one, two or all three of the main branches of coronary artery could get involved critically. Sometimes these fatty lumps (plaque) breaks creating a surface for blood clot formation and complete occlusion of the vessel. The prolonged deprivation of blood supply results in death of the muscle (necrosis).