Cardiac arrest strikes immediately and without warning. The victim becomes unresponsive suddenly and collapses. Typically, the victim does not respond when called and shaken gently. The breathing pattern is usually abnormal, and the victim may stop breathing completely. This results in the skin color becoming dusky or blue after a few minutes because of the lack of oxygen. Movements that resemble a seizure may be seen. There are no signs of circulation, and no pulse can be detected. Recognizing the signs of a cardiac arrest is an essential first step in activating the Chain of Survival, followed by notifying emergency medical services by calling 911. This is then followed by early CPR when needed, early defibrillation when indicated, and early advanced medical care.