When medical professionals speak about heart attacks they are usually referring to a ‘coronary’, or a blockage in one of the heart’s blood vessels. This usually causes chest pain, but it only causes collapse or sudden death in perhaps a quarter of all people who get a blockage. The medical name for a ‘heart attack’ is a myocardial infarction, often shortened as ‘MI’. Cardiac arrest is when the heart stops beating effectively due to a sudden serious change in the heart’s rhythm. This always results in collapse, and often in sudden death. Defibrillators (including the automatic external defibrillators, or AEDs, available in many public places) can be used to treat some but not all causes of cardiac arrest.