CPR should be performed when someone is unresponsive and not breathing normally. These two signs together indicate cardiac arrest, meaning the heart has stopped pumping blood effectively. Every minute without CPR reduces the chance of survival, so recognizing these signs quickly is the single most important skill a bystander can have.
The Two Signs That Call for CPR
The decision to start CPR comes down to two observations: the person doesn’t respond when you shout at them or tap their shoulders, and they aren’t breathing normally. You don’t need to check for a pulse. Feeling for a pulse is unreliable under stress, and the seconds spent searching for one are seconds without blood flow to the brain. If someone is unconscious and not breathing, call 911 and begin chest compressions immediately.
For children, tap their shoulder and shout their name. For infants, tap the bottom of the foot. If there’s no response within about 10 seconds, and you see no normal breathing, start CPR.
Why Gasping Doesn’t Count as Breathing
One of the most common reasons bystanders hesitate is that the person appears to still be breathing. In many cardiac arrests, the victim will gasp, snore, gurgle, or make moaning sounds. This is called agonal breathing, and it is not real breathing. It’s a reflex triggered by the brain as oxygen runs out, and it typically stops within about four minutes.
Bystanders frequently tell 911 dispatchers that the person is breathing when they hear these sounds, which delays lifesaving instructions. If someone is unconscious and the only “breathing” you notice is irregular gasping, snorting, or gurgling, treat it as cardiac arrest. Start compressions.
Cardiac Arrest vs. Heart Attack
A heart attack happens when blood flow to the heart is blocked, usually by a clot. The person is typically conscious, may complain of chest pain, and is still breathing. A heart attack does not require CPR. What it requires is a fast call to 911 so the blockage can be treated at a hospital.
Cardiac arrest is different. The heart’s electrical system malfunctions and the heart stops beating entirely. The person collapses, loses consciousness, and stops breathing within seconds. CPR is the only thing that keeps blood circulating until the heart can be restarted. A heart attack can trigger cardiac arrest, which is why someone having a heart attack needs monitoring. If they lose consciousness and stop breathing, that’s when CPR begins.
How Bystander CPR Changes Survival
The numbers here are striking. A 2024 American Heart Association analysis found that people who received bystander CPR within two minutes of cardiac arrest had an 81% greater chance of surviving to hospital discharge and a 95% higher chance of surviving without significant brain damage, compared to those who received no bystander CPR at all. Even CPR started up to 10 minutes after collapse improved survival by 19%.
The brain begins to suffer irreversible damage after about four to six minutes without oxygen. Emergency medical services in most cities take 8 to 12 minutes to arrive. That gap is why bystander CPR matters so much. You are the bridge between collapse and professional care.
How to Perform Chest Compressions
The 2025 American Heart Association guidelines recommend pushing hard and fast on the center of the chest. For adults, compress at least 5 centimeters deep (about 2 inches) but no deeper than 6 centimeters. Push at a rate of 100 to 120 compressions per minute, which is roughly the tempo of the song “Stayin’ Alive.” Let the chest fully recoil between each compression so the heart can refill with blood.
If you’re untrained or uncomfortable giving rescue breaths, hands-only CPR (continuous chest compressions without mouth-to-mouth) is the current recommendation for bystanders. The AHA specifically encourages this approach because it simplifies the process and removes one of the biggest barriers to action: reluctance to perform mouth-to-mouth on a stranger. For most adult cardiac arrests, uninterrupted compressions are more valuable than pausing to deliver breaths.
Trained rescuers, particularly those responding to drowning, drug overdose, or pediatric cardiac arrest, should provide rescue breaths alongside compressions. These situations involve oxygen deprivation as the root cause, so ventilation plays a larger role. For drowning specifically, the international resuscitation guidelines recommend that trained responders like lifeguards consider giving rescue breaths first before starting compressions, while untrained bystanders should still begin with compressions.
Using an AED Alongside CPR
An automated external defibrillator (AED) can restart a heart that’s in an abnormal rhythm. If one is available nearby, send someone to grab it while you continue compressions. Do not stop CPR to go find an AED yourself unless no one else is present and the device is within a few seconds’ reach.
Once the AED arrives, turn it on and follow the voice prompts. The device will analyze the heart rhythm and tell you whether a shock is needed. After delivering the shock (or if no shock is advised), immediately resume CPR for about two minutes before the AED checks the rhythm again. Keep cycling between compressions and AED checks until emergency services arrive or the person starts showing obvious signs of life, like normal breathing.
When to Stop CPR
Once you start, don’t stop unless one of these things happens:
- The person starts breathing normally and shows clear signs of life.
- An AED is powered on and ready to analyze the rhythm.
- Emergency medical personnel arrive and take over.
- Another trained person takes over so you can rest.
- You are physically too exhausted to continue effective compressions.
- The scene becomes unsafe (fire, structural collapse, traffic).
Good compressions are tiring. Quality drops significantly after about two minutes of continuous effort. If a second rescuer is available, switch every two minutes to keep compressions strong.
Legal Protection for Bystanders
Every U.S. state has some form of Good Samaritan law that protects people who provide emergency care in good faith. If you crack a rib during CPR (which happens frequently, even when the technique is perfect), these laws provide a legal defense against liability. The protection covers honest mistakes that a reasonable person might make while trying to help. It does not cover intentional harm or reckless behavior, but performing CPR on someone in cardiac arrest falls squarely within the kind of emergency response these laws were written to encourage.