Eventually, plaque buildup that is not treated properly may completely block an artery. This can occur either because the plaque itself becomes so thick or because it leads to a blood clot, called a thrombus.
As plaque deposits grow, they may crack or tear. When this happens, blood naturally begins to clot in the area. The blood can form a clot on the plaque's surface that's large enough to fully block the artery. If this happens in one of your heart's arteries, called the coronary arteries, it causes a heart attack. A heart attack is also called a myocardial infarction.
Because of tears in plaque and blood clots, a 30% blockage of your arteries can suddenly threaten your life. During a heart attack, the part of your heart that isn't getting oxygen begins to die. In some cases, the damage cannot be reversed.