Cardiac arrest is when the interruption of normal circulation of the blood due to failure of the heart. It is also different from a heart attack but can still be caused by a heart attack.
A heart attack is where the blood flow to the still-beating heart is interrupted.

When the circulation of the blood prevents the  delivery of oxygen to all the organs of the body. A lack of oxygen to the brain can cause lack of consciousness and normal breathing is stopped. Lack of Brain function is likely to occur if in cardiac arrest for more than five minutes.

Cardiac arrest can be reversible in some patients if treated early enough. If the cardiac arrest leads to death it is called sudden cardiac death. CPR can be administered until emergency help can arrive; however it usually takes a defibulator to bring someone back from cardiac arrest