The severity of arterial atherosclerosis is related to the location of the lesion and the narrowing it causes in the coronary arteries. This is because if the blood flow through the coronary arteries is insufficient to meet the metabolic demands of the heart muscle, it can lead to ischemia and hypoxia of the heart muscle, causing angina. Severe and prolonged ischemia can lead to myocardial necrosis, or myocardial infarction. When there is significant narrowing in the coronary artery lumen, for instance more than 50%-75%, the situation can be compensated during rest. However, during exercise or rapid heart rate or emotional excitation, the oxygen demand of the heart muscle increases. This may result in mild or transient myocardial oxygen supply, or an imbalance between supply and demand. Another scenario involves unstable atherosclerotic plaques that rupture, erode, or bleed, leading to platelet aggregation or thrombus formation, causing a rapid worsening of luminal narrowing. This results in a decreased supply of oxygen to heart muscle, leading to acute coronary syndrome, which is very severe. In fact, the degree of coronary artery atherosclerosis is positively correlated with plaque stability, plaque location, and the elasticity of the coronary artery.