What is the difference between a MI and a cardiac arrest?

A myocardial infarction is an event caused by a blockage in an artery which damages the heart muscle. A cardiac arrest is an event that may be caused by a myocardial infarction or may be caused by other events such as respiratory failure or electrolyte abnormalities which causes the heart to go into an unstable rhythm. In this rhythm the heart cannot pump effectively, so treat the cause.