You should perform CPR when someone is unresponsive and not breathing normally. Those two signs together point to cardiac arrest, and every minute without chest compressions reduces the chance of survival by 7 to 10 percent. You don’t need to be certain. If the person has collapsed, won’t respond when you shout or tap their shoulders, and isn’t breathing or is only making occasional gasping sounds, start CPR immediately after calling 911.
The Two Signs That Tell You to Start
Current American Heart Association guidelines boil the decision down to two things: consciousness and breathing. If an adult is unconscious and not breathing normally, you should assume they are in cardiac arrest and begin chest compressions. You do not need to check for a pulse. Accurately detecting a pulse is difficult even for trained medical professionals, and fumbling for one wastes critical seconds.
Tap the person firmly on the shoulders and shout, “Are you okay?” If there’s no response, look at their chest for five to ten seconds. Normal breathing means a steady, visible rise and fall. If you see nothing, or if the person is only gasping, groaning, or making snoring-like sounds, that counts as “not breathing normally” and CPR should begin.
Don’t Be Fooled by Gasping
One of the most common reasons bystanders hesitate is that the person appears to still be breathing. Agonal gasps, the irregular, labored sounds a body makes in the first minutes of cardiac arrest, are frequently mistaken for real breathing. They’ve been described as snoring, gurgling, moaning, or snorting. They can look and sound alarming, but they are not effective breaths. The heart has stopped, and the brain is running out of oxygen.
This confusion has real consequences. Bystanders who hear gasping often tell 911 dispatchers the person is breathing, which can lead to delayed or incorrect instructions. If the person is unconscious and those sounds are the only “breathing” you see, treat it as cardiac arrest. Starting compressions on someone who turns out not to need them is far less dangerous than waiting while someone’s brain goes without blood flow.
Cardiac Arrest vs. Heart Attack
These two emergencies are often confused, but they call for very different responses. A heart attack is a circulation problem: a blocked artery cuts off blood supply to part of the heart muscle. The person is typically conscious, may complain of chest pain, shortness of breath, or nausea, and their heart is still beating. They need 911 and fast transport to a hospital, but they do not need CPR unless they lose consciousness and stop breathing.
Cardiac arrest is an electrical problem. The heart’s rhythm becomes chaotic or stops entirely, and the person collapses, loses consciousness, and has no pulse within seconds. This is the situation that demands CPR. It’s worth knowing that a heart attack can trigger cardiac arrest, so if someone having heart attack symptoms suddenly becomes unresponsive and stops breathing, the situation has changed and you should begin compressions.
Special Situations: Drowning and Overdose
For most adults who collapse from a cardiac cause, hands-only CPR (continuous chest compressions without rescue breaths) works well. But some situations are different. In drowning and drug overdoses, the problem starts with breathing failure rather than an electrical malfunction of the heart. The body runs out of oxygen first, and the heart stops second.
For someone pulled from the water, the AHA’s updated guidelines recommend that trained rescuers start with two rescue breaths before beginning 30 chest compressions, then continue that cycle. Research shows drowning victims are more likely to survive when CPR includes rescue breaths compared to compressions alone. If you’re not trained or not comfortable giving breaths, compressions alone are still far better than doing nothing. One important note: CPR should be started before using an AED if one is available, and an AED should only be applied after the person has been removed from the water.
Opioid overdoses follow a similar logic. Breathing stops first, so rescue breaths paired with compressions give the best chance. If naloxone (the overdose-reversal medication) is available, administer it, but if the person remains unresponsive and isn’t breathing normally, begin CPR while waiting for emergency services.
Children and Infants
The trigger for CPR in children and infants is the same core assessment: unresponsive and not breathing normally. One additional consideration applies to trained rescuers caring for infants or small children. If a child has a pulse but it’s very slow, below 60 beats per minute, and they’re showing signs of poor circulation such as pale or bluish skin, chest compressions should be started even though the heart hasn’t fully stopped. A heart rate that low in a child often can’t maintain adequate blood flow on its own.
For children, rescue breaths are especially important because pediatric cardiac arrests more commonly result from breathing problems rather than heart rhythm failures. If you’re trained, use the 30 compressions to 2 breaths ratio for a single rescuer, or 15 to 2 if a second rescuer is available.
When Not to Perform CPR
There are a small number of situations where CPR should not be started. If the person has injuries that are clearly incompatible with life, such as catastrophic trauma, CPR will not help. If the person has a valid do-not-resuscitate order and you’re aware of it, that legal document should be respected.
You should also stop CPR if continuing puts your own life in danger, for example in an active fire, structural collapse, or other escalating hazard. Your safety comes first.
When to Stop Once You’ve Started
Once you begin CPR, keep going until one of these things happens: emergency medical services arrive and take over, the person starts breathing normally and becomes responsive, an AED is ready to deliver a shock (pause compressions only long enough to use it, then resume), or you become physically unable to continue. CPR is exhausting. If another bystander is available, switch off every two minutes to keep compressions effective.
Why Every Minute Counts
The survival math is stark. Without any CPR, the chance of surviving cardiac arrest drops by roughly 7 to 10 percent with every passing minute. With bystander CPR, that decline slows to about 3 to 4 percent per minute. Brain damage begins within four to six minutes of oxygen deprivation. By the time an ambulance arrives, which averages eight to twelve minutes in most areas, the window may already be closing. Bystander CPR is the bridge that keeps blood and oxygen moving until professional help takes over.
Legal Protections for Bystanders
Every U.S. state has some form of Good Samaritan law designed to protect people who provide emergency care in good faith. These laws generally shield you from civil liability as long as you act voluntarily, don’t accept payment, and don’t engage in reckless or intentionally harmful behavior. Cracking a rib during chest compressions, which happens regularly even when CPR is performed correctly, falls under ordinary negligence and is protected. The specific details vary by state, but the core principle is consistent: if you’re genuinely trying to help in an emergency, the law is on your side.