In the sudden cessation of normal heart rhythm leading to abrupt cessation of blood circulation called "cardiac arrest", the conducting system of the heart fails to produce or conduct electrical impulses that cause the heart to contract and supply blood to the body. Sudden cardiac arrest is a medical emergency; first-aid treatment such as cardiopulmonary resuscitation (CPR) and defibrillation (delivering a dose of electrical energy to the heart) can improve the chances of survival. If not treated, cardiac arrest leads to sudden cardiac death.