According to the American Heart Association, Acute Coronary Syndrome (ACS) is any group of clinical symptoms that are compatible with acute myocardial ischemia. Acute myocardial ischemia is chest pain due to insufficient blood supply to the heart muscle that results from coronary artery disease. For additional information about ACS, please see the links below:

americanheart.org - American Heart Association
nhlbi.nih.gov - National Heart Lung & Blood Institute
worldheart.org - World Heart Federation