Although brief but it can give you an insight view : Cardiac arrest: A medical emergency with absent or inadequate contraction of the left ventricle of the heart that immediately causes bodywide circulatory failure. The signs and symptoms include loss of consciousness; rapid shallow breathing progressing to apnea (absence of breathing); profoundly low blood pressure (hypotension) with no pulses that can be felt over major arteries; and no heart sounds. Cardiac arrest is one of the greatest of all medical emergencies. Within several minutes, there is lack of oxygen (tissue hypoxia), leading to multiple organ injury. Unless cardiac arrest is quickly corrected, it is fatal. The most common causes of cardiac arrest are electrical problems in the heart with ventricular fibrillation representing the major type. In ventricular fibrillation, there is loss of coordinated ventricular contractions leading to immediate loss of effective output of blood by the heart, resulting in circulatory arrest.