Witnessing a cardiac arrest resuscitation attempt can be one of the most distressing experiences of your life. One moment someone is fine, the next they have collapsed, unresponsive, while people around them fight to keep them alive. The sights and sounds of that scene can stay with you long afterwards.
This page explains what happens at the scene of a resuscitation attempt and why. Understanding what you saw, and knowing that much of it was a normal bodily response to the heart stopping, can be an important step in coming to terms with it. If you were there, whether you acted, called for help, or froze, this page is for you.
What the scene can look like
A cardiac arrest is sudden. The person collapses and becomes unresponsive, sometimes injuring themselves as they fall. They may gasp, moan, vomit, or twitch as the body reacts to the loss of a heartbeat. For family, friends, and bystanders, it is a frightening and chaotic few minutes.
When paramedics arrive, the activity intensifies. They check for a pulse and breathing, attach a defibrillator, and may give oxygen, medications, and other treatments. Clothing is often cut away. It can look rough and impersonal, but every action is deliberate and time-critical. The team is working against the clock to restart the heart and protect the brain.
Equipment used
At an out-of-hospital cardiac arrest, you may see some or all of the following:
- Defibrillator (AED): a portable device that analyses the heart rhythm and, if appropriate, delivers a shock to try to restore a normal rhythm. Public AEDs give spoken instructions so anyone can use them.
- Oxygen: given through a face mask or a tube to support breathing.
- Intubation equipment: a laryngoscope to visualise the airway and a tube placed into the windpipe to help the person breathe.
- Medications: drugs such as adrenaline, given to support the heart and circulation.
- Cardiac monitor: continuously tracks the heart rhythm so the team can see how the person is responding.
- IV fluids: given through a line in a vein to support blood pressure and circulation.
- Suction: used to clear vomit or secretions from the airway.
- Stretcher and transport equipment: once the person is stable enough, they are moved to hospital for further treatment.
ECMO
ECMO, or Extracorporeal Membrane Oxygenation, is essentially a heart-lung bypass machine. It takes over the work of delivering oxygen to the body when the heart and lungs cannot do it themselves. It is used in a small number of very serious cases, usually in hospital, to give the heart and lungs a chance to rest and recover. It is a temporary measure that can buy precious time.
Vomiting
Vomiting is common during a cardiac arrest. When the heart stops, the muscles that normally keep the stomach contents down relax, and the pressure of chest compressions can push air into the stomach and force its contents up. It can make CPR harder for the person giving it, which is why responders are taught to roll the person and clear the airway if needed.
Vomiting is a symptom of the arrest, not a cause of it, and it does not mean anything was done wrong.
Foam
Foam around the mouth happens when air mixes with saliva and fluid in the airway. Gasping, chest compressions moving air in and out of the lungs, and relaxed throat muscles allowing saliva to pool can all contribute. It can look alarming, but it is a recognised and normal feature of cardiac arrest.
Blood in the mouth
Blood in or around the mouth can have several causes:
- A bitten tongue or cheek: the person may have bitten themselves as they collapsed or during seizure-like movements.
- Injury from the fall: a knock to the face or mouth as they went down.
- Pulmonary oedema: fluid building up in the lungs, which can be blood-tinged and come up into the mouth.
- Vomiting or aspiration: stomach contents or fluids brought up or inhaled can carry blood with them.
Body movements during CPR
Chest compressions mimic the pumping action of the heart, and the whole upper body moves with each one. The chest and abdomen rise and fall as air is pushed out of the lungs and the heart is squeezed. This movement is normal and is actually a sign that compressions are being done with enough force to circulate blood. CPR should continue, however dramatic the movement looks, until professional help takes over.
Twitching, gasping, and seizure-like movements
When the brain is starved of oxygen, it can produce involuntary movements. The person may twitch, jerk, or appear to have a seizure. They may also take slow, gasping breaths known as agonal breathing or agonal gasps. These gasps are a brain stem reflex, not normal breathing, and they are a sign that the person is in cardiac arrest and needs CPR immediately.
These movements can be deeply confusing for witnesses. Many people hesitate to start CPR because the gasping or twitching looks like a sign of life. It is not. If someone is unresponsive and not breathing normally, start CPR.
Mioklonie
Myoclonus describes sudden, brief, jerky muscle movements that can affect any part of the body. It is caused by the brain reacting to a lack of oxygen and blood flow, and it can occur during an arrest or in the hours and days afterwards in hospital. Doctors monitor it closely because it can give them information about how the brain is recovering.
Skin colour changes
When the heart stops pumping, oxygen-rich blood no longer reaches the skin. The person may quickly turn pale, blue, grey, or mottled. The change is often most visible in the lips and fingertips, where the skin is thinnest, and may be more obvious in people with lighter skin tones. It is one of the clearest outward signs of cardiac arrest and a signal that immediate action is needed.
Soiling
During a cardiac arrest, the muscles that control the bladder and bowel can relax along with the rest of the body, and the person may lose control of them. It does not happen in every case, but when it does, it is simply the body’s response to the heart stopping. It is nothing to do with weakness or dignity, and experienced responders treat it as the routine medical event it is.
Eyes
The eyes can change noticeably during a cardiac arrest. They may appear dull or glassy, with pupils that are dilated and unresponsive to light. They may be open, half open, rolled back, or fluttering as a result of involuntary muscle movements. For many witnesses, the eyes are the most haunting memory of the scene. These changes reflect the brain being deprived of oxygen, and they vary from person to person.
Rib or chest injuries
Effective chest compressions need to push the breastbone down by at least 5 to 6 centimetres. That amount of force can crack or break ribs, particularly in older people or those with weaker bones. You may have heard or felt a crack while performing CPR, and it can be a memory that lingers.
Rib fractures are painful, but they heal, and they are rarely life threatening. Compressions that are too gentle do not circulate blood to the brain and vital organs. If ribs broke during CPR, it almost always means the compressions were done properly. Broken ribs should never be a reason to hold back from CPR. The alternative is far worse.
Zoning out and tunnel vision
Many lay responders describe a strange narrowing of the world during a resuscitation attempt. They could not hear sirens, did not notice people arriving, or have gaps in their memory of the event. This is often called tunnel vision, and it is a normal stress response.
In a sudden emergency, the body floods with adrenaline and the brain focuses all of its resources on the task in front of it. Everything else, sounds, surroundings, the passage of time, can simply fall away. Fear, shock, lack of training, and sheer mental exhaustion all add to the effect. If your memory of the scene feels patchy or unreal, that is your brain doing what brains do under extreme stress, not a failing on your part.
Why did I freeze?
Some people freeze when they witness a cardiac arrest. Freezing is one of the brain’s built-in responses to sudden, overwhelming danger, alongside fight and flight. It is involuntary. Fear, the shock of seeing someone collapse, and not knowing what to do can all trigger it, and no amount of caring about the person can override a hardwired survival reflex.
If you froze, you may be carrying guilt, replaying the scene and wondering what might have been different. Please know that freezing was not a choice, and it says nothing about your character or courage. Many people in our community have stood exactly where you are standing, and talking about it helps.
Getting support after witnessing a resuscitation attempt
Witnessing or taking part in a resuscitation attempt is a traumatic event, whatever the outcome. Intrusive memories, disturbed sleep, anxiety, and replaying the scene are all normal reactions in the weeks that follow. If they persist or start to interfere with everyday life, support is available and it works.
- Read about trauma after cardiac arrest and the support routes on our counselling page.
- If you were close to the person, our page for co-survivors explains the impact a cardiac arrest has on those around it.
- Connect with people who understand by joining our community of survivors, co-survivors, and rescuers.
Frequently asked questions
What do Abbott (formerly St Jude) ICD alerts mean?
Abbott ICDs (formerly St Jude Medical) have traditionally alerted you by vibration rather than sound. A typical pattern is a six-second vibration, then sixteen seconds of silence, then a further six-second vibration, then ten seconds of silence, after which the pattern repeats.
Historically, many Abbott devices had no patient alert at all. The newer Gallant models have added an audible alert facility, so a Gallant device may beep as well as vibrate.
If you feel an unexpected vibration from your device, contact your ICD clinic, and ask for a demonstration at your next appointment. Our ICD sounds and alerts page explains the alerts by manufacturer.
Category: Implantable DevicesWhat do Boston Scientific ICD alert sounds mean?
Boston Scientific ICDs use audible alert tones. A typical alert is a set of sixteen tones that repeats roughly every six hours until the device is checked.
It is worth knowing that having an MRI scan permanently disables the beeper on these devices. If that applies to you, your clinic will usually recommend relying on remote monitoring so that alerts are still picked up.
If you hear an alert, contact your ICD clinic. To hear what your device sounds like, ask for a demonstration at a clinic visit. Our ICD sounds and alerts page has more detail.
Category: Implantable DevicesWhat do Medtronic ICD alert sounds mean?
Medtronic ICDs can alert you with both audible tones and vibration. A common pattern is a six-second vibration, then sixteen seconds of silence, then a further six-second vibration, then ten seconds of silence, after which the pattern repeats.
A solid, continuous tone is the magnet alert tone, which you may hear when a magnet is placed over the device. These tones are programmable, so your clinic can adjust them or switch them off, and your own device may sound different.
If you hear an alert, contact your ICD clinic. To hear exactly what your device sounds like, ask for a demonstration at your next appointment. Our ICD sounds and alerts page has example recordings.
Category: Implantable DevicesDo all ICDs make sounds, or does every ICD beep?
No. Whether your ICD makes a sound depends on the manufacturer, the model, and how it has been programmed. Some devices beep, some vibrate, some do both, and some make no patient alert at all.
For example, Medtronic devices use audible tones and vibration, Boston Scientific devices use audible tones, and Abbott devices have historically used vibration, with audible alerts on the newer Gallant models. Biotronik and Sorin/Microport devices do not emit patient alerts and rely on remote monitoring instead.
If you are not sure what your device does, ask for a demonstration at your next clinic appointment. Our ICD sounds and alerts page lists the alerts by manufacturer.
Category: Implantable DevicesWhat does a low-battery alert from my ICD mean?
A low-battery alert means your ICD’s battery is approaching the end of its life. The device emits a warning sound periodically, usually at the same time of day, so you may notice it as a regular daily beep.
This warning typically begins three to six months before the battery is depleted, so it is not an emergency. Contact your ICD clinic so they can check the device and plan a replacement, known as a generator or box change.
Our ICD sounds and alerts page explains the common alert types in more detail.
Category: Implantable Devices