Acute myocardial infarction (AMI or MI), commonly known as a heart attack, is a serious, sudden heart condition usually characterized by varying degrees of chest pain or discomfort, weakness, sweating, nausea, vomiting, and arrhythmias, sometimes causing loss of consciousness. It occurs when the blood supply to a part of the heart is interrupted, causing death and scarring of the local heart tissue. Since the area affected may be large or small, the severity of heart attacks vary, but they are often a life-threatening medical emergency which demand both immediate attention and activation of the emergency medical services.
Diagnosis is by the combination of medical history, ECG findings and blood tests for cardiac enzymes. The most important treatment in myocardial infarction is restoring the blood flow to the heart, by thrombolysis (enzymatically dissolving the clot in the artery) and/or angioplasty (using a balloon to push the artery open). Close monitoring on a coronary care unit is mandatory to observe for various complications. There is emphasis on secondary prevention, the elimination of risk factors that could lead to further heart attacks.
The medical term myocardial infarction derives from myocardium (the heart muscle) and infarction (tissue death), in this case caused by an obstruction of blood flow. The phrase "heart attack" is occasionally used to refer to heart problems other than a myocardial infarction, such as unstable angina pectoris.