A defibrillator is a life-saving machine that gives the heart an electric shock in some cases of cardiac arrest. This is called defibrillation and can save lives. Cardiac arrest is when the heart stops pumping blood around the body. When someone has a cardiac arrest, defibrillation needs to be prompt. For every minute that passes without defibrillation chances of survival decrease by 10%. Research shows that applying a controlled shock within 4 minutes of collapse, combined with High Quality CPR, Provides the best possible chances of survival.