Acute coronary syndrome is most often a complication of plaque buildup in the arteries in your heart (coronary atherosclerosis) These plaques, made up of fatty deposits, cause the arteries to narrow and make it more difficult for blood to flow through them.
Eventually, this buildup means that your heart can't pump enough oxygen-rich blood to the rest of your body, causing chest pain (angina) or a heart attack. Most cases of acute coronary syndrome occur when the surface of the plaque buildup in your heart arteries ruptures and causes a blood clot to form. The combination of the plaque buildup and the blood clot dramatically limits the amount of blood flowing to your heart muscle. If the blood flow is severely limited, a heart attack will occur.