Sudden cardiac arrest is a leading cause of premature death, but with immediate treatment many lives can be saved. Sudden cardiac arrest occurs because the electrical rhythm that controls the heart is replaced by a chaotic disorganised electrical rhythm called ventricular fibrillation. Seconds count, and the ambulance service is unlikely to arrive quickly enough to resuscitate most victims. However, a defibrillator can be used which gives a high energy electric shock to restore the heart’s normal rhythm. In an emergency, you should ring 999 and the operator will advise where the nearest defibrillator is, and talk you through the process.