The term heart attack refers to damage to the muscle of the heart, usually from a lack of blood flow. Most of the time a blood clot forms in one of the arteries that supply heart muscle with blood, blocking the flow of blood. As the heart muscle starves it begins to die, causing chest pain and other heart attack symptoms.
Cardiac arrest happens when the heart stops pumping blood. With no pumping action, the blood pressure falls and blood is no longer forced into the muscles and organs of the body. There are all sorts of reasons the heart will stop pumping blood. It might get extremely weak or begin quivering uselessly. It might also start racing so fast it can no longer fill with blood, which causes the blood pressure to fall dangerously.
Recognize a heart attack and get help immediately to avoid cardiac arrest. Don't hesitate to call an ambulance for things like chest pain. If a victim collapses in front of you and stops breathing, he or she is likely in cardiac arrest and needs CPR.