You should perform CPR when someone is unresponsive and not breathing normally. Those two signs together indicate cardiac arrest, and every minute without chest compressions reduces the person’s chance of survival by 7 to 10 percent. You don’t need to be certain about what caused the collapse. If the person won’t respond when you tap their shoulders and shout, and they aren’t breathing or are only gasping, start CPR.
The Two Signs That Tell You to Start
Cardiac arrest recognition comes down to checking two things. First, responsiveness: tap the person firmly on the shoulders and ask loudly if they’re OK. If they don’t move, speak, blink, or react in any way, they’re unresponsive. Second, breathing: watch their chest for normal rise and fall. If the chest isn’t moving, or if the person is only making occasional gasping or gurgling sounds, they need compressions immediately.
That gasping pattern trips up a lot of bystanders. It can sound like snoring, moaning, or snorting, and it’s easy to mistake for actual breathing. It’s not. It’s called agonal breathing, and it’s a sign the brain is still alive but the heart has stopped doing its job. People who are gasping actually have a high chance of surviving if you start chest compressions right away. If your compressions cause someone who stopped gasping to start again, that’s a good sign. Keep going.
Agonal breathing typically stops within about four minutes of cardiac arrest. If you wait to see whether someone “starts breathing on their own,” you may lose the window where CPR is most effective.
You Don’t Need to Check for a Pulse
Current guidelines no longer expect untrained bystanders to check for a pulse before starting CPR. Even healthcare professionals frequently misjudge whether a pulse is present, especially under stress. The two-check approach, unresponsive plus no normal breathing, is reliable enough to act on. If both signs are present, begin chest compressions.
Specific Situations That Call for CPR
Sudden Cardiac Arrest
This is the most common scenario. Someone collapses without warning, often in a public place, at home, or during physical activity. Their heart has gone into an abnormal rhythm and stopped pumping blood. Hands-only CPR (continuous chest compressions without rescue breaths) is effective here because the person’s blood still carries oxygen from their last few breaths. Push hard and fast on the center of the chest, and have someone call 911 and grab an AED if one is nearby.
When bystander CPR is started promptly, the survival rate drops by only 3 to 4 percent per minute instead of 7 to 10 percent. That difference is enormous over the 8 to 12 minutes it typically takes for paramedics to arrive.
Drowning
Drowning works differently from a typical cardiac arrest. The heart stops because the person ran out of oxygen, not because of a heart rhythm problem. Their blood is already depleted, so chest compressions alone won’t move useful oxygen to the brain. If you’re trained in rescue breathing, the recommended approach is to give two rescue breaths first, then begin cycles of 30 chest compressions followed by two breaths. If you’re not trained in rescue breathing, compression-only CPR is still better than doing nothing.
Opioid Overdose
When someone has overdosed on opioids, their breathing slows and can stop entirely. If the person is unresponsive and not breathing, start CPR immediately. If you have naloxone (the overdose-reversing nasal spray available at most pharmacies), administer it, but not at the expense of pausing chest compressions. CPR comes first. Naloxone is given alongside compressions, not instead of them. If the person is still breathing, even slowly or irregularly, and is not fully awake, naloxone alone may be enough, but watch them closely for any change.
Choking That Leads to Unconsciousness
If someone who was choking loses consciousness and stops breathing, the situation shifts from abdominal thrusts to CPR. Lower the person onto their back on a firm surface. Open their mouth and look for a visible object you can remove. If you can’t see anything or the chest doesn’t rise when you attempt rescue breaths, begin chest compressions. The force of compressions can help dislodge whatever is blocking the airway. After every 30 compressions, check the mouth again for the object before giving two more breaths.
Infants and Children
Children and infants more often experience cardiac arrest from breathing problems rather than heart rhythm issues, similar to drowning. CPR that includes rescue breaths is especially important for kids. For trained rescuers helping a child or infant, compressions should begin if the heart rate drops below 60 beats per minute and the child shows signs of poor circulation, like pale or bluish skin, even after you’ve been helping them breathe. For any child who is unresponsive and not breathing, the same rule applies as adults: start CPR.
Check the Scene Before You Start
Before you kneel down next to someone, take a few seconds to scan for danger. This isn’t bureaucratic caution. If the person collapsed because of a gas leak, a downed power line, or an active traffic lane, rushing in without looking could put both of you at risk. Move the person only if the immediate area is unsafe. Otherwise, perform CPR right where they are, on the firmest surface available.
When to Stop Performing CPR
Once you start, keep going. Bystander CPR should continue until one of a few things happens: emergency medical services arrive and take over, an AED is ready to use and prompts you to stop for a shock, or the person starts breathing normally and becomes responsive. Fatigue is real during chest compressions, so if another bystander is available, trade off every two minutes to keep the compressions effective. Don’t stop because the person gasps. That’s a sign CPR is working.
The core message is simple. If someone is unresponsive and not breathing normally, they need chest compressions now. You cannot make the situation worse by starting CPR on someone in cardiac arrest, but you can absolutely make it worse by waiting.