When someone is unconscious and not responding, you may be witnessing cardiac arrest, and CPR should begin immediately once you confirm the person isn’t breathing normally. Every minute without chest compressions reduces the chance of survival. People who receive bystander CPR before paramedics arrive have a 28% greater chance of surviving compared to those who don’t, according to data from the National Institutes of Health.
How to Tell If Someone Needs CPR
Finding someone unconscious doesn’t automatically mean they need CPR. The first step is to tap their shoulders firmly and shout, “Are you okay?” If there’s no response at all, call 911 (or have someone nearby call) and then check for breathing. Kneel beside the person, place your ear near their mouth and nose, and look at their chest. You’re doing three things at once: looking for the chest to rise and fall, listening for air escaping, and feeling for breath against your cheek. This whole check should take no more than 10 seconds.
If the person isn’t breathing, or is only making occasional gasping sounds, treat it as cardiac arrest and start CPR right away. Those gasping sounds, called agonal breaths, can fool people into thinking someone is still breathing adequately. They’re not. Agonal breathing is a reflex that happens in the early minutes of cardiac arrest, and it does not deliver oxygen to the body.
If you’re not a trained healthcare professional, skip checking for a pulse entirely. Research has shown that untrained rescuers frequently misjudge pulse checks, either feeling their own pulse or missing a faint one. The American Heart Association removed the pulse check from lay rescuer training for this reason. If the person is unconscious, unresponsive, and not breathing normally, that’s your signal to begin compressions.
Starting Chest Compressions
Place the heel of one hand in the center of the person’s chest, right on the breastbone. Stack your other hand on top and interlock your fingers. Keep your arms straight, lock your elbows, and position your shoulders directly above your hands so your body weight does the work. Push hard and fast, compressing the chest at least 2 inches deep for an adult, at a rate of 100 to 120 pushes per minute. That pace is roughly the tempo of the song “Stayin’ Alive,” which is a genuinely useful mental metronome.
Let the chest fully recoil between each compression. This is easy to forget when you’re pushing fast, but it matters. The recoil creates a slight vacuum inside the chest that pulls blood back into the heart, refilling it before the next push. Leaning on the chest between compressions reduces blood flow significantly.
Even perfect chest compressions deliver only 10% to 30% of normal blood flow to the heart and 30% to 40% of normal blood flow to the brain. That sounds low, but it’s enough to keep brain cells and heart tissue alive until a defibrillator or paramedics can restore a normal rhythm. Without compressions, that blood flow drops to zero.
Compressions Only vs. Compressions With Breaths
The current guideline is 30 chest compressions followed by 2 rescue breaths, then repeat. To give breaths, tilt the person’s head back by pushing gently on the forehead while lifting the chin with your other hand. This moves the tongue away from the back of the throat and opens the airway. Pinch the nose shut, seal your mouth over theirs, and blow steadily for about 1 second, watching for the chest to rise. Give two breaths, then return to compressions immediately.
If you’re unwilling or unable to give rescue breaths, do hands-only CPR (compressions without stopping). A large randomized trial published in the New England Journal of Medicine found no significant difference in survival to hospital discharge between compression-only CPR and traditional CPR with breaths: 12.5% survived with compressions alone versus 11.0% with compressions plus breathing. For cardiac arrests caused by heart problems specifically, compression-only CPR actually trended toward better outcomes, with 15.5% survival compared to 12.3%.
The takeaway is simple: compressions are the most critical part. If giving breaths feels like a barrier to starting CPR at all, skip them and push. Uninterrupted chest compressions are far better than no CPR while you hesitate.
Using an AED
If an automated external defibrillator is available nearby, send someone to grab it while you continue compressions. Don’t stop CPR to go looking for one yourself unless you’re alone and it’s within a few steps. When the AED arrives, turn it on and follow the voice prompts. The device will talk you through every step, including where to place the adhesive pads on the person’s bare chest.
The AED analyzes the heart’s rhythm and determines whether a shock is needed. Not all cardiac arrests involve a rhythm that responds to defibrillation, so the device may tell you “no shock advised.” That doesn’t mean the person is fine. It means you should resume chest compressions immediately and keep going. If a shock is advised, the AED will instruct you to press a button and will warn everyone to stand clear first. After the shock, go right back to compressions.
Continue alternating between CPR and following the AED’s prompts until paramedics take over or the person starts showing clear signs of life, such as breathing normally, coughing, or moving purposefully.
When to Stop CPR
Keep performing CPR until one of three things happens: emergency medical services arrive and take over, the person begins breathing normally and moving on their own, or you become physically unable to continue. CPR is exhausting. If another bystander is available, switch off every two minutes to keep the quality of compressions high. Tired rescuers push shallower without realizing it.
Signs that the person may be recovering include spontaneous breathing, coughing, gagging, or purposeful movement like reaching or turning. If you see these signs, stop compressions, keep the person on their side to protect their airway, and monitor them closely until help arrives. They can deteriorate again quickly.
Legal Protection for Bystanders
Many people hesitate to perform CPR because they’re afraid of being sued, especially if they crack a rib (which happens frequently during proper compressions, particularly in older adults). Good Samaritan laws exist in every U.S. state specifically to address this fear. These laws protect bystanders who voluntarily provide emergency care from civil liability, as long as they act in good faith and don’t do something recklessly dangerous.
Breaking a rib during CPR is considered ordinary negligence at most, and Good Samaritan laws explicitly cover that kind of unintentional injury. What these laws don’t protect is gross negligence: performing CPR on someone who is clearly breathing normally, or attempting medical procedures far beyond your training. As long as you’re genuinely trying to help someone who appears to be in cardiac arrest, and you’re not accepting payment for it, you’re protected. The legal risk of performing CPR is essentially zero. The risk of not performing it, for the person on the ground, is death.