How Long Does Brain Activity Last After Cardiac Arrest?

Cardiac arrest is a catastrophic event in which the heart stops beating. This means the body is deprived of the oxygen it needs to survive. The American Heart Association reports that more than 356,000 out-of-hospital cardiac arrests occur in the United States each year. Nearly 90% of them are fatal.

Beyond the high risk of death, one major concern is the impact of prolonged oxygen deprivation on the brain and the damage that can occur within three minutes of the heart stopping.

This article explores what happens when oxygen is cut off to the brain during a cardiac arrest, and the common symptoms seen when a person is revived. It also looks at problems that arise when blood flow begins again in tissues that are damaged.

Man in cardiac arrest in the rain with medics preforming CPR
Bruce Ayres / Getty Images

What Happens During Cardiac Arrest

A person becomes unconscious quickly during cardiac arrest. This usually happens within 20 seconds after the heart stops beating. Without the oxygen and sugars it needs to function, the brain is unable to deliver the electrical signals needed to maintain breathing and organ function.

This can lead to a hypoxic-anoxic injury (HAI). Hypoxia refers to a partial lack of oxygen, while anoxia means a total lack of oxygen. In general, the more complete the oxygen loss, the more severe the harm to the brain.

With cardiac arrest, all parts of the the brain that rely on blood flow are affected by its failure. An injury caused by anoxia is called diffuse brain damage. Among the parts of the brain most vulnerable to injury is the temporal lobe, where memories are stored.


When cardiac arrest occurs, cardiopulmonary resuscitation (CPR) must be started within two minutes. After three minutes, global cerebral ischemia—the lack of blood flow to the entire brain—can lead to brain injury that gets progressively worse.

By nine minutes, severe and permanent brain damage is likely. After 10 minutes, the chances of survival are low.

Even if a person is resuscitated, eight out of every 10 will be in a coma and sustain some level of brain damage. Simply put, the longer the brain is deprived of oxygen, the worse the damage will be.

If you haven't learned CPR recently, things have changed. You can usually find a two- to three-hour training course at a local community health center, or by contacting a Red Cross or American Heart Association office in your area.

Resuscitation and Symptoms

People are most likely to be successfully revived in a hospital or another site with quick access to defibrillators. These are devices that send electrical impulses to the chest to restart the heart. These devices are found in many workplaces, sports arenas, and other public places.

When a cardiac arrest is treated very quickly, a person may recover with no signs of injury. Others may have mild to severe damage.

Memory is most profoundly affected by apoxia, so memory loss will often be the first sign of the damage. Other symptoms, both physical and psychiatric, may be obvious, while some may only be noticed months or years later.

For those who are resuscitated and are not in a coma, apoxia may cause:

  • Severe memory loss (amnesia)
  • Involuntary muscle contractions (spasticity)
  • Loss of muscle control
  • Loss of mobility and fine motor control
  • Incontinence
  • Impaired speech
  • Changes in personality
  • Disorientation as to place, person, or time

Some symptoms may improve over time. Others, however, may be lasting and require a person to be under lifelong assisted care.


Some 90% of people who go into cardiac arrest outside of a hospital—meaning at home, work, or wherever it occurs—will die. Even when the heart is restarted and blood flow begins delivering oxygen to the cells again, most people will still have serious impacts. These impacts, like memory loss or mobility issues, are worse the longer the brain is deprived of oxygen.


People who are comatose after a cardiac arrest will often have damage to different parts of the brain, such as the:

Even the spinal cord will sometimes be damaged. People who are in a coma for 12 hours or more will usually have lasting problems with thinking, movement, and sensation. Recovery will often be incomplete and slow, taking weeks to months.

The most severely affected people may end up in a vegetative state, more appropriately known as unresponsive wakefulness syndrome (UWS). The eyes may open in people with UWS, and voluntary movements may occur, but the person does not respond and is unaware of their surroundings.

Some 50% of people with UWS caused by a traumatic brain injury will regain consciousness. Unfortunately, those with UWS due to lack of oxygen more often don't.

Reperfusion Injury

Restoring the flow of blood through the body is called reperfusion. It is key to reviving the person and preventing or limiting brain damage. But when this occurs, the sudden rush of blood to areas of damaged tissues can cause injury.

It may seem counterintuitive because restarting the flow of blood is the critical goal. But the lack of oxygen and nutrients during the time of cardiac arrest means that when blood flow is restored, it places oxidative stress on the brain as toxins flood already-damaged tissues.

The inflammation and nerve injury this causes can trigger a cascade of symptoms, including:

  • Severe headaches or migraines
  • Seizures
  • Weakness or paralysis on one side of the body
  • Vision loss or blindness in one eye
  • Difficulty understanding things heard or spoken
  • Loss of awareness of one side of your environment (hemispatial neglect)
  • Slurred or jumbled speech
  • Dizziness or vertigo
  • Double vision
  • Loss of coordination

The severity of these symptoms is closely linked to how long the person went without oxygen. Other factors include any pre-existing conditions affecting the brain and cardiovascular system.


When the heart stops, so does the flow of blood that's pumped throughout the body. Brain damage will begin in a matter of minutes because of the lack of oxygen carried by the blood cells.

Cardiac arrest is usually fatal outside of a hospital setting, but even those who are revived may have severe and lasting impacts. It's important to act quickly to restart the heart and limit these catastrophic effects.

A Word From Verywell

All brain activity is thought to cease by around three to four minutes from the moment the heart stops. Thus, every second counts if someone suddenly collapses in front of you and stops breathing.

Rather than wasting time putting the victim in the car and rushing to the hospital, call 911 and start hands-only CPR immediately. You may buy enough time until the paramedics arrive to restart the heart.

Frequently Asked Questions

  • How long can the brain go without oxygen?

    It can take less than five minutes of oxygen deprivation for some brain cells to start dying. Cerebral hypoxia, or when there is a lack of oxygen reaching the brain, can cause brain damage and become fatal after a short amount of time.

  • How long can someone be in a coma?

    It is rare for someone to be in a coma for longer than two to four weeks. However, there have been very rare cases of people who have stayed in a coma for multiple years, or even decades. Brain damage becomes more likely the longer that a person is in a coma.

  • What happens during cardiac arrest?

    During cardiac arrest, a person's heart stops beating and they shortly become unconscious. Their breathing stops and organs cease to function. If CPR is not performed within two to three minutes of cardiac arrest, brain injury can become worse. After nine minutes, brain damage is extremely likely. Since blood and oxygen are not able to reliably reach the brain, the chance of surviving cardiac arrest after 10 minutes is very low.

3 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Benjamin EJ, Virani SS, Callaway CW, et al. Heart disease and stroke statistics-2018 update: a report from the American Heart Association. Circulation. 2018;137(12):e67-e492. doi:10.1161/CIR.0000000000000558

  2. MedlinePlus. Cerebral Hypoxia.

  3. National Institute of Neurological Disorders and Stroke. Coma Information Page.

Additional Reading