Angina is caused by reduced blood flow to the heart resulting in the heart muscle not receiving enough oxygen. The pain is often triggered by overactivity or stress. There are two types of angina, stable and unstable, of which stable angina, or chronic ischemic heart disease, is more common.

The electrocardiogram of coronary artery disease will provide indirect information about the presence, extent and severity of some coronary artery diseases. Recent studies have analyzed ST segment changes to provide useful information in acute coronary syndromes and myocardial infarction.