New plaque tends to be soft, but is prone to rupturing.
Plaque rupture can trigger the formation of a blood clot. Old plaque tends to have a lot of calcium and to be hard, which makes it somewhat less likely to rupture. Atherosclerosis affects large and medium-sized arteries. The type of artery involved and the location of the plaque varies with each person. Atherosclerosis is a slow, progressive disease that may start as early as childhood.