Risk factors such as age, diabetes, hypertension, smoking, high blood cholesterol levels and family history can cause lipid (fatty) materials to clog these small diameter coronary arteries and form what are known as plaques (little humps of fatty material with some calcium deposits making them hard) on the inside lumen the artery. As the size of the plaque increases, the arteries start to narrow or stenose.
When one or more of these arteries get blocked the blood supply is reduced to the area of the heart muscle resulting in lack of nutrients and oxygen supply especially during exercise or exertion. This is often called "Coronary artery disease" [CAD] or "Atherosclerotic Heart disease".
Most people start experiencing chest pains or other symptoms like fatigue or shortness of breath when the block is over 50%. As the block gets narrower, symptoms increase either in intensity or frequency or both. Heart attack or Myocardial Infarction occurs when the artery is completely occluded and the muscles die.
ECG, Treadmill, Echocardiogram will be done to diagnose CAD. Angiogram is done to show the accurate percentage of blocks in each artery.