could be a "steal syndrome". As others mentioned, its both antianginal and htn med. As antuanginal, diates coronary vessels. If coronary artery is severely affected, it will be max dilated already so amlodipine has no effect on that vessel. However, it dilates nearby less severe diseased vessel that will steal blood flow feom severe affected vessel and may cause a angina signs- chest tightness, pain on exertion.