The technical name for heart disease is coronary artery disease which we will also refer to as CAD. Blood is constantly flowing through the heart which is busy pumping the blood throughout the body. CAD is a disease that causes damage to the arteries that are busy providing the blood flow. In other words the disease affects the arteries. It does this by constricting the arteries. It impairs them. The blood delivers the life giving oxygen and nutrients which removes the waste products from the blood including carbon dioxide.

Look at the above diagram, do you see the plaque build-up along the walls of the artery. This plaque constricts the artery or makes it smaller in diameter. This means that the blood cannot flow through the artery as easily it could if there were no plaque deposits blocking the blood supply from flowing. This is also why some heart patients feel pain in their chest upon any kind of exertion. The blood needs to flow through the heart arteries. If you are exercising than you need that blood to flow through more quickly. Since the artery is being partially blocked by plaque, your entire system cannot get the blood it needs, and therefore you are experiencing pain from the constricted blood flow.

Perhaps you will get a better understanding of the process of what plaque and blockages can do by looking at the picture below. In this picture how much of the flow of the blood is interrupted by the plaque buildup or blockage. It looks like only about 50% of the blood can make it through the artery to the other side of the blockage.

If you look at the lower right hand portion of the picture, you are looking at a cross section of the artery. It is clear that only about half the blood supply can make it through this artery. This is what heart disease is. It is a blockage (one or more) in the arteries of the heart.