Version July 2025
Please read the Disclaimer at the end of this page.
What is sudden cardiac arrest? —
Sudden cardiac arrest, or "SCA," is when the heart suddenly stops beating. It is a medical emergency that needs to be treated right away. SCA that isn't treated right away causes death (called "sudden cardiac death"). But even with treatment, most people with SCA do not survive.
The heart has a built-in electrical system that keeps it beating in a normal rhythm. In SCA, a problem happens with the electrical system. This leads to an abnormal heart rhythm. The abnormal heart rhythm that happens most often in SCA is called "ventricular fibrillation," or "V-fib." In this rhythm, the lower chambers of the heart (called "ventricles") twitch, but do not pump blood (figure 1).
What causes SCA? —
SCA is most likely to happen in people who already have a heart problem, whether they know about it or not. Heart problems that can cause SCA include:
●"Coronary artery disease" – This is when the arteries that bring blood to the heart get clogged with fatty deposits.
●A heart attack
●"Cardiomyopathy" – This is thickening of the heart muscle.
●Other problems with the heart's electrical system
●Heart failure – This is when the heart doesn't pump as well as it should.
Other conditions and events that can also cause SCA include:
●Certain lung problems
●A severe injury, drowning, or getting electrocuted
●Illegal drugs, such as cocaine, heroin, or methamphetamine ("meth")
●Electrolyte problems – Electrolytes are substances (like sodium or potassium) that the body needs to work normally.
What are the symptoms of SCA? —
Many people do not have any "warning" symptoms before SCA. But up to half of people do have symptoms before. These can happen either just before SCA, or in the days leading up to it. Symptoms might include:
●Chest pain or trouble breathing
●Feeling like the heart is racing, skipping beats, or beating out of sync
●Feeling weak or dizzy
When SCA happens, a person loses consciousness, has no pulse, and is not breathing.
How is SCA treated? —
SCA needs to be treated right away with both:
●Cardiopulmonary resuscitation, or "CPR" – This is a way to get blood and oxygen moving through the body of someone whose heart has stopped beating. It involves "compressions," which is when another person presses hard and fast (over and over again) on the person's chest. This squeezes the heart and gets blood moving again, although not as well as when the heart pumps blood on its own.
●Defibrillation – This involves using a device to send an electrical shock to the heart. This shock can sometimes get a normal heart rhythm started again. Defibrillation has the best chance of working when it is done right away.
If these treatments are done within a few minutes of SCA, they sometimes work to restart the heart. After the heart is beating again and blood is flowing through the body, the person will get further treatment and tests.
Doctors or emergency workers sometimes start a treatment called "hypothermia" to cool the body down. This can give people a better chance of surviving in the days after SCA. For this treatment, the body is cooled down to a few degrees below normal for 1 to 2 days. This helps reduce brain injury. This is important, because brain injury is the most common cause of death after SCA.
Most people need a breathing tube. This is a tube that goes down the throat and into the lungs. The other end is attached to a machine that helps with breathing.
Your doctor will also look for the cause of your SCA and treat it, if it can be treated. To look for the cause, your doctor will do a lot of tests. These usually include:
●Electrocardiogram, or "ECG" – This measures the electrical activity in the heart (figure 2).
●Chest X-ray
●Blood tests
●Echocardiogram, or "echo" – This uses sound waves to create pictures of the heart as it beats (figure 3).
●Other imaging tests – These create pictures of the inside of the body.
Your doctor might decide to do a procedure called cardiac catheterization, or "cardiac cath." The doctor puts a thin tube into a blood vessel in your leg or arm. Then, they move the tube up to your heart. When the tube is in place, the doctor can do tests or unblock a clogged artery (figure 4).
Most people who survive SCA are also treated with an implantable cardioverter-defibrillator, or "ICD." This is a device that goes under the skin near the heart. It can sense abnormal heartbeats and then treat them with an electrical shock.
What will my life be like if I survive? —
It depends, in part, on what caused the SCA and how quickly it was treated. Some people recover completely without any long-term problems. But many people have long-term brain problems.
Patient education: Coronary artery disease (The Basics)
Patient education: Ventricular fibrillation (The Basics)
Patient education: Heart attack (The Basics)
Patient education: What can go wrong after a heart attack? (The Basics)
Patient education: Heart failure (The Basics)
Patient education: ECG and stress test (The Basics)
Patient education: Echocardiogram (The Basics)
Patient education: Cardiac catheterization (The Basics)
Patient education: Implantable cardioverter-defibrillators (The Basics)
Patient education: CPR for adults (The Basics)
Patient education: CPR for children (The Basics)
Patient education: Advance directives (The Basics)
Patient education: Heart attack (Beyond the Basics)
Patient education: Heart failure (Beyond the Basics)
Patient education: Stenting for the heart (Beyond the Basics)
Patient education: Implantable cardioverter-defibrillators (Beyond the Basics)
