Atherosclerosis is deposits of calcium-laced cholesterol. It happens to everybody over time, and as we age we get more of it. It only becomes a problem when there's so much in one place that it impedes, or obstructs, the flow of blood through it. In that case, tissue reliant on the blood will slowly die. It it's heart muscle, that muscle will die, and the result is a (usually) painful heart attack (myocardial infarction).

The treatments that I know of are those meant to stabilize plaque and to help to slow the deposition rate, and that is a statin. Or, they can bypass that blocked area with a stent, or an angioplasty to try to widen the narrowed part. This is all quite involved, and you can read lots about it all by doing a search like:

'treatment for atherosclerosis.'