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Cardiac arrest can strike without warning

Do you suspect someone is experiencing cardiac arrest? The signs are:

  • Sudden loss of responsiveness – The person doesn’t respond, even if you tap them hard on the shoulders or ask loudly if they’re OK. The person doesn’t move, speak, blink or otherwise react.
  • No normal breathing – The person isn’t breathing or is only gasping for air.

What Causes Cardiac Arrest?

Cardiac arrest may be caused by any heart condition. Most cardiac arrests occur when a heart’s electrical system malfunctions causing an abnormal heart rhythm. Some cardiac arrests are also caused by extreme slowing of the heart’s rhythm.

Common causes of cardiac arrest include:

  • Scarring of the heart tissue – It may be the result of a prior heart attack or another cause. A heart that’s scarred or enlarged from any cause is prone to develop life-threatening ventricular arrhythmias. The first six months after a heart attack is a high-risk period for sudden cardiac arrest in patients with atherosclerotic heart disease.
  • Thickened heart muscle (cardiomyopathy) – Damage to the heart muscle can be the result of high blood pressure, heart valve disease or other causes. A diseased heart muscle can make you more prone to sudden cardiac arrest, especially if you also have heart failure. Learn more about cardiomyopathy.
  • Heart medications – Under certain conditions, some heart medications can set the stage for arrhythmias that cause sudden cardiac arrest. (Oddly, antiarrhythmic drugs that treat arrhythmias can sometimes produce ventricular arrhythmias even at normal doses. This is called a “proarrhythmic” effect.) Significant changes in blood levels of potassium and magnesium (from using diuretics, for example) also can cause life-threatening arrhythmias and cardiac arrest.
  • Electrical abnormalities – These, including Wolff-Parkinson-White syndrome and Long QT syndrome, may cause sudden cardiac arrest in children and young people.
  • Blood vessel abnormalities – These rare cases occur particularly in the coronary arteries and aorta. Adrenaline released during intense physical activity can trigger sudden cardiac arrest when these abnormalities are present.
  • Recreational drug use – This can occur in otherwise healthy people


What to do if  you suspect a person is experiencing cardiac arrest?

If you think the person may be suffering cardiac arrest and you’re a trained lay rescuer:

  • Ensure scene safety.
  • Check for response.
  • Seek help. Tell someone nearby to call 911 or your emergency response number. Ask that person or another bystander to bring you an AED (automated external defibrillator), if there’s one on hand. Remain calm, but stress that time is critical.
  • Check for no breathing or only gasping. If the person isn’t breathing or is only gasping, begin CPR with compressions.
  • Begin high quality CPR. Push down at least two inches in the center of the chest at a rate of 100 to 120 pushes a minute. Allow the chest to come back up to its normal position after each push.
  • Use an AED. As soon as it arrives, turn it on and follow the prompts.
  • Continue CPR. Administer it until the person starts to breathe or move, or until someone with more advanced training, such as an EMS team member, takes over.

Cardiac Arrest Resources


Source: American Heart Association, last reviewed January 29, 2021.