Sudden Cardiac Arrest: Why It Happens

Medically Reviewed by James Beckerman, MD, FACC on February 01, 2016
3 min read

You collapse without warning. Your heart stops beating, and blood stops flowing to your brain and other organs. Within seconds, you stop breathing and have no pulse. This is sudden cardiac arrest.

The immediate cause of most sudden cardiac arrests is an abnormal heart rhythm. The heart’s electrical activity becomes chaotic, and it can’t pump blood to the rest of the body.

Conditions that can trigger sudden cardiac arrest include:

Coronary artery disease. This is the most common cause of sudden cardiac arrest in people older than 35.

Cardiomyopathy. When you have this condition, your heart muscle becomes enlarged or thick, so it's weakened.

Long QT syndrome and Brugada syndrome. These disorders of the heart’s electrical system can cause abnormal heart rhythms.

Marfan syndrome. This inherited disorder can cause parts of the heart to stretch and become weak.

Heart birth defects. Even if you have had surgery to correct a defect, you are still at risk for sudden cardiac arrest.

Other things that can raise your chance include:

Being male

  • Age -- the risk is higher for men after age 45 and for women after age 55
  • A previous cardiac arrest or heart attack
  • A family history of cardiac arrest or heart disease


With quick action, you can survive sudden cardiac arrest. CPR needs to begin immediately, and treatment with an automated external defibrillator (AED) within a few minutes.

“Every second counts,” says Gregg Fonarow, MD, cardiology professor at UCLA's David Geffen School of Medicine.

Call 911 if you have:

  • Chest pain
  • Discomfort in one or both arms or in the back, neck, or jaw
  • Unexplained shortness of breath

If someone you are with shows signs of a sudden cardiac arrest, call 911 or ask someone else to call. Be calm, and check to see if the person is able to respond to you. Start doing CPR right away if they are unconscious and are not breathing. CPR will keep the blood circulating to the brain and other organs. You can stop if they begin breathing, or when emergency medical services arrive and take over.

While you're doing CPR, get someone else to look for an automated external defibrillator (AED) and use it immediately. An AED is a portable device that sends an electric shock through the chest to the heart when needed. The shock can restore a normal rhythm to the heart. There are AEDs in many public places, like shopping malls, airports, hotels, and schools.

Talk with your doctor.

There are steps you can take to lower your risk. Your doctor may recommend medication, surgery, or other treatments or lifestyle changes. Someone in your household should be trained in CPR and in the use of an AED.

A device called an ICD (implantable cardioverter-defibrillator) can help prevent sudden cardiac arrest in some people who are at high risk. The device usually goes under the skin in your upper chest. It monitors your heart rhythm. If it detects an irregular rhythm, it uses electrical pulses or shocks to restore a normal rhythm.

Sudden cardiac arrest sometimes happens in people who have no known heart condition or any previous symptoms.

“But studies show that people who survive cardiac arrest often realize later that they had symptoms they were ignoring. If they had sought treatment, they might have been able to prevent the sudden cardiac arrest,” Fonarow says.

Sometimes, sudden cardiac arrest strikes seemingly healthy athletes. In these cases, it often turns out that the athlete had an undiagnosed condition, such as cardiomyopathy.

Christine Lawless, MD, former co-chair of the American College of Cardiology’s Sports and Exercise Cardiology Section & Leadership Council, suggests that athletic teens and young adults get tested for potential heart problems.

The American Heart Association recommends a 12-point screening test that looks at family and personal history, along with a physical exam. An electrocardiogram (ECG) can also identify heart conditions that can put people at risk.

Finding those problems early "may prevent catastrophic cardiac events such as sudden cardiac arrest,” Lawless says.