Cardiac arrest is the sudden loss of blood flow throughout the body resulting from the heart not being able to pump blood efficiently. It is a rapidly fatal medical emergency requiring immediate intervention with cardiopulmonary resuscitation (CPR) until further treatment can be provided. Cardiac arrest results in rapid loss of consciousness and breathing may be abnormal or absent.

Cardiac monitoring in the ED setting has a primary focus on the monitoring of arrhythmia, myocardial infarction, and QT-interval monitoring. It is a noninvasive diagnostic tool and monitoring is categorized by the rating system developed by the American College of Cardiology Emergency Cardiac Care Committee. The different classes are as follows: