A 20% narrowing of the coronary arteries is not normal. In normal people, the coronary arteries have smooth walls and smooth blood flow. Coronary artery stenosis is the narrowing of the coronary artery lumen due to atherosclerosis. In normal people, the walls of the coronary arteries are smooth and the blood flow is smooth, so stenosis will not occur. If coronary artery stenosis is detected through coronary angiography, coronary artery disease can basically be diagnosed. Depending on the degree of coronary artery stenosis, it can be categorized as mild to moderate to severe. If the degree of coronary stenosis does not exceed 50%, it is mild coronary stenosis and can be treated with internal medicine. If the degree of coronary artery stenosis is around 50% to 70%, it is called moderate stenosis. Most patients with severe stenosis will have clinical manifestations. If the degree of stenosis is more than 75%, the stenosis is severe. Aggressive treatment with stenting or coronary artery bypass grafting is required. Coronary artery stenosis requires prompt medical attention and treatment with medication under the direction of a doctor to improve the blood supply.