A stent can be implanted if there is clear evidence of ischemia in a major coronary vessel (greater than 2 mm in diameter) of the heart with a stenosis of 75% or more and a left main stem stenosis of greater than 50%. It is also possible to choose whether to implant a stent by measuring the velocity of blood flow or by testing an angiographic ultrasound to see the exact situation. However, the specific index is currently based on 75%, and if clear evidence of ischemia exists in the patient, stent implantation or coronary artery bypass therapy is required. Cardiac angiography is the gold standard for the diagnosis of coronary artery disease, for which a stenosis of 50% or more of the blood vessels is found. If clear evidence of ischemia is present, a stent can be implanted if the vessel is stenosed at 75% or more.