Someone in cardiac arrest is unconscious, unresponsive, and either not breathing or only gasping irregularly. Those three signs are all you need to recognize it. Unlike a heart attack, which can build slowly with chest pain and shortness of breath, cardiac arrest strikes without warning. A person who seemed fine seconds ago suddenly collapses, and their heart has stopped pumping blood. Brain activity flatlines within 15 to 30 seconds, which is why recognizing it fast matters more than being perfectly certain.
The Three Signs to Look For
The American Heart Association recommends that non-medical bystanders skip the pulse check entirely. Accurately detecting a pulse is surprisingly difficult, even for trained professionals, and fumbling at someone’s wrist or neck wastes critical seconds. Instead, you’re looking for three things:
- Unresponsive. The person doesn’t react when you tap their shoulders and shout at them. They can’t be woken up.
- Not breathing normally. Their chest isn’t rising and falling in a steady rhythm. They may not be breathing at all, or they may be making occasional gasps (more on that below).
- No signs of life. No movement, no coughing, no response of any kind.
If someone is unconscious and not breathing normally, the official guidance is to assume cardiac arrest and act immediately. Waiting for more proof costs time the person doesn’t have.
Why Gasping Doesn’t Mean They’re Breathing
The most common mistake bystanders make is seeing someone gasp and assuming they’re still breathing. This is called agonal breathing, and it’s a reflex, not real respiration. The person may make occasional, labored gasps. Their face might grimace as if they’re in pain. But they are almost certainly unconscious, and the gasping is not delivering oxygen to their brain or organs.
This is exactly the scenario 911 dispatchers are trained to cut through. Their protocol asks two key questions: “Is the patient conscious?” and “Is he or she breathing normally?” If the answer to both is no, they begin walking you through CPR instructions immediately. Gasping, gurgling, or infrequent breaths all count as “not breathing normally.”
How Cardiac Arrest Differs From a Heart Attack
People use these terms interchangeably, but they describe different emergencies. A heart attack is a plumbing problem: a blocked artery cuts off blood flow to part of the heart muscle. The heart keeps beating, and the person is usually conscious, often experiencing chest pain, arm pain, or shortness of breath. Heart attack symptoms can come on gradually, sometimes over hours.
Cardiac arrest is an electrical problem. The heart’s rhythm short-circuits, causing it to quiver uselessly or stop altogether. Blood flow to the brain, lungs, and every other organ ceases instantly. The person loses consciousness within seconds. There is no slow onset, no warning pain. One moment they are standing; the next they are on the ground.
A heart attack can trigger cardiac arrest if the damage to the heart muscle disrupts its electrical system, which is one reason heart attacks are treated so urgently. But many cardiac arrests happen in people who had no chest pain or prior symptoms at all.
Why Every Minute Counts
When the heart stops, blood stops reaching the brain. Consciousness disappears within about 10 to 20 seconds. Brain cells begin dying within minutes. The longer the brain goes without oxygen, the less likely the person is to survive with their neurological function intact.
Bystander CPR bridges that gap by manually pushing blood through the body until a defibrillator or paramedics arrive. The numbers are stark: people who receive bystander CPR before an ambulance arrives have roughly a 10% chance of surviving to hospital discharge, compared to about 5.5% for those who don’t. That may sound modest, but it represents a 24% higher likelihood of survival. For every minute without CPR, the odds drop further.
What Causes It
In most adults, cardiac arrest traces back to coronary artery disease. Years of plaque buildup can create the conditions for a fatal rhythm disturbance, sometimes without the person ever knowing they had heart disease. Prior heart attacks, heart failure, and thickening of the heart muscle all raise the risk.
In younger people, the causes tend to be different: inherited rhythm disorders, inflammation of the heart muscle, or structural abnormalities present from birth. Some of these conditions produce no symptoms until the moment of arrest, which is why cardiac arrest occasionally strikes seemingly healthy young athletes.
What to Do Once You Recognize It
Call 911 first, or have someone nearby do it while you start CPR. Push hard and fast in the center of the chest, about two compressions per second. You don’t need to do rescue breaths if you’re not trained in them. Hands-only CPR is effective and far better than doing nothing.
If an automated external defibrillator (AED) is available, use it as quickly as possible. These devices are designed for untrained bystanders. You attach the pads, and the machine analyzes the heart’s rhythm automatically. It will only deliver a shock if it detects one of the specific rhythm problems that a shock can fix. You cannot accidentally shock someone who doesn’t need it.
Keep doing chest compressions between AED prompts and until paramedics take over. Even imperfect CPR is dramatically better than standing by. The person is already in the worst possible situation. You cannot make it worse by trying.