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The heart is like a home; it runs on plumbing and electricity. A heart attack, or AMI, is a problem with the plumbing of the heart, when blood flow within cardiac arteries is blocked, usually by a clot.

Sudden cardiac arrest is a problem with the electrical signals that tell the heart muscle when to beat and how much blood to pump. Sudden cardiac arrest is just that: a sudden, immediate loss of heart function. A person suffering sudden cardiac arrest, which is usually caused by ventricular fibrillation, also stops breathing and loses consciousness. The electrical disturbance stops blood flow to the rest of the body, a condition that can be fatal.

Some people have chronic problems with the electrical signals in their heart muscle; those conditions, which include atrial fibrillation, can often be treated with ablation procedures or other modern techniques. Sudden cardiac arrest, though, is a medical emergency that must be treated immediately.

While sudden cardiac arrest is different from a heart attack, a heart attack can sometimes trigger an electrical disturbance that leads to sudden cardiac arrest.

Symptoms of sudden cardiac arrest

The symptoms of sudden cardiac arrest are sudden and drastic: a person collapses, has no pulse, stops breathing immediately and loses consciousness. Sometimes people may experience symptoms before sudden cardiac arrest (fainting, blackouts, dizziness, chest pain, shortness of breath, weakness, palpitations, vomiting), but most cases occur suddenly and without warning.

What to do for sudden cardiac arrest

  • Call 911. If you’re alone and find someone unconscious with no pulse, administer chest compressions for two minutes, then call 911.
  • Administer CPR. If you don’t know CPR, just push hard and fast on the person's chest – about two compressions a second or 100 a minute. Allow the chest to rise completely between compressions. Continue chest compressions until a portable defibrillator is available or emergency personnel arrive.
  • Use a portable defibrillator if one is available. The device, also called an automated external defibrillator, is easy to use, and most have audible directions to guide you through the process. 911 operators also can help you use the device.