The most common cause of sudden cardiac arrest is ischemic heart disease. The risk of sudden death is increased with worsening atherosclerotic coronary arterial narrowing. However, the first event with an acute coronary syndrome is typically an arrhythmia, and this is why resuscitation, including defibrillation, can be successful, and survivors may have no ECG or enzyme changes to suggest myocardial infarction has occurred. Inflammation with infarction or infection takes days to develop. Sudden valvular incompetence from papillary muscle rupture, or wall rupture, may complicate an infarction 3 to 7 days following the initial event.