- The Chain of Survival.

 The Chain of Survival.

The series of actions linking the victim of sudden cardiac arrest with survival are called the "Chain of Survival".

All four links of the chain must be strong.

They are:

1. Early recognising those at risk of cardiac arrest and calling for help in the hope that early treatment can prevent arrest.
2. Early Cardiopulmonary resuscitation (CPR) to buy time,performing chest-compression-only CPR is better than giving no CPR at all (1)(2) , CPR should be provided immediately after collapse of the patient (3)(4) , Properly performed CPR can keep the heart in a shockable ventricular fibrillation for 10–12 minutes longer (5) ,CPR keeps blood flowing to the heart, brain and throughout the body, sustaining life until a defibrillator, or other advanced medical care, arrives.
3. Early defibrillation, to restart the heart,this step is often called the critical link in the Chain of Survival, because treatment with an automated external defibrillator(AED) can restore a normal beat to a heart quivering from SCA by delivering a measured electrical shock. 
4. Post-resuscitation care: to restore the quality of life

References:

1. SOS-KANTO Study Group. Cardiopulmonary resuscitation by bystanders with chest compression only (SOS-KANTO): an observational study. Lancet 2007;369:920–6.
2. Iwami T, Kawamura T, Hiraide A, et al. Effectiveness of bystander-initiated cardiac-only resuscitation for patients with out-of-hospital cardiac arrest. Circulation 2007;116:2900–7.
3. "Part 12: From Science to Survival - Strengthening the Chain of Survival in Every Community," Circulation 2000;102:I-358
4. Eisenberg MS, Bergner L, Hallstrom A (1979). "Cardiac resuscitation in the community. Importance of rapid provision and implications for program planning". JAMA 241 (18): 1905–7. doi:10.1001/jama.241.18.1905. PMID 430772.
5.Bossaert LL (1997). "Fibrillation and defibrillation of the heart". British journal of anaesthesia 79 (2): 203–13. PMID 9349131