For most people, their internal cholesterol gauge works well enough to keep their cholesterol at a good level.
However, if your levels of cholesterol are too high, LDLs will leave extra cholesterol in the blood. If the HDL's cannot pick up all of this cholesterol, it will begin to build up on your artery walls, along with other fats and debris. This build up is called plaque. Over time, plaque can narrow the blood vessels and sometimes this build up may even block your blood vessels completely. Plaque build up on your blood vessel walls is called atherosclerosis.
A narrowed or blocked blood vessel can prevent blood from getting to where it needs to go.
If the blocked vessel is in your brain, it can cause a stroke. Blockages can also happen in the blood vessels, called the coronary arteries, that carry blood to the heart muscle. This blockage process is called coronary heart disease, and the end result can be a heart attack.