Acute coronary syndromes result from a sudden blockage in a coronary artery. This blockage causes unstable angina or heart attack (myocardial infarction), depending on the location and amount of blockage. People who experience an acute coronary syndrome usually have chest pressure or ache, shortness of breath, and fatigue. People who think they are experiencing an acute coronary syndrome should call for emergency help and then chew an aspirin tablet. Doctors use electrocardiography and measure substances in the blood to determine whether a person is experiencing an acute coronary syndrome. Treatment varies depending on the type of syndrome but usually includes attempts to increase blood flow to affected areas of the heart.