You should start CPR whenever someone is unresponsive, not breathing normally, and doesn’t have a pulse. In most cases, this means the person is in cardiac arrest, and every minute without chest compressions reduces their chance of survival. When CPR begins within the first minute, about 22% of people survive to leave the hospital. By 10 minutes without CPR, that number drops to roughly 10%.
The Three Signs That Call for CPR
Cardiac arrest can look different from what you’d expect. The person may collapse suddenly or may have been sitting still and simply stopped responding. The signs you’re looking for are straightforward:
- No responsiveness. The person doesn’t react when you tap their shoulders and shout at them.
- No normal breathing. They’re either not breathing at all, or they’re making irregular gasping sounds (more on this below).
- No pulse. Current guidelines actually tell untrained bystanders to skip the pulse check entirely and focus on responsiveness and breathing instead. Checking for a pulse under stress is unreliable, and the delay costs precious seconds.
If someone meets the first two criteria, call 911 and start chest compressions immediately. You don’t need to be certain it’s cardiac arrest. Starting CPR on someone who doesn’t technically need it carries far less risk than withholding it from someone who does.
How to Recognize Agonal Breathing
One of the most common reasons bystanders hesitate is because the person appears to still be breathing. In many cardiac arrests, the body produces what’s called agonal gasping, an involuntary reflex that can sound like snoring, gurgling, moaning, or snorting. These gasps are irregular and labored. They are not signs of life in any meaningful sense.
Agonal breathing is actually a sign of cardiac arrest, not a reason to hold off. If someone is unresponsive and making these sounds, they need CPR. Interestingly, performing chest compressions on someone who has stopped gasping can sometimes cause the gasping to resume, which is a positive sign that blood is still circulating.
Why Every Minute Counts
A large U.S. study published in the AHA’s journal Circulation found a clear, graded relationship between CPR delay and death. Compared to people who received CPR within one minute, those who waited just 2 to 3 minutes were 9% less likely to survive. At 4 to 5 minutes, the odds of survival dropped by 27%. The same pattern held for neurological outcomes, meaning not just surviving but surviving with brain function intact.
The reason is simple: when the heart stops pumping, the brain and other organs lose their blood supply. Chest compressions act as a manual pump, pushing blood through the body and keeping enough pressure in the arteries to deliver oxygen to the brain and heart muscle. Without that circulation, organ damage begins within minutes and becomes irreversible quickly.
Hands-Only CPR vs. Rescue Breaths
For most bystanders witnessing a sudden cardiac arrest in an adult, hands-only CPR (compressions without mouth-to-mouth breathing) is the recommended approach. Research shows that for cardiac causes of arrest, continuous chest compressions alone produce outcomes comparable to traditional CPR with rescue breaths. The key is not stopping compressions, since every pause lets blood pressure in the heart drop.
There are situations where rescue breaths matter more. Drowning, drug overdose, choking, and suffocation all cause arrest because of an oxygen problem, not a heart rhythm problem. In these cases, the blood is already low on oxygen, so breathing for the person provides a meaningful benefit. The same applies to children and infants, whose cardiac arrests are more often caused by breathing problems than by heart rhythm issues. If you’re trained in full CPR with rescue breaths, use that training in these scenarios.
Correct Compression Technique for Adults
Place the heel of one hand on the center of the chest, right on the breastbone. Put your other hand on top, interlace your fingers, and press straight down. The target depth is at least 2 inches, and your rate should be 100 to 120 compressions per minute. A common reference is the beat of the song “Stayin’ Alive.”
Let the chest fully recoil between each compression. Leaning on the chest between pushes prevents the heart from refilling with blood, which defeats the purpose. If you’re getting tired, which happens faster than most people expect, switch off with another bystander every two minutes if possible. Fatigue causes compressions to become too shallow, and most people don’t realize their quality is declining.
Differences for Children and Infants
For children ages 1 to 8, use the heel of one hand placed on the breastbone just below the nipple line. Compress to about one-third to one-half the depth of the chest. The rate stays the same at 100 to 120 per minute.
For infants under 1 year, use two fingers placed on the breastbone just below the nipple line. The same depth ratio applies: compress about one-third the depth of the chest. Because pediatric arrests are more likely to involve a breathing problem, rescue breaths are more important here. The standard cycle is 30 compressions followed by 2 gentle breaths.
When to Stop CPR
As a bystander, you should keep performing CPR until one of three things happens: emergency medical services arrive and take over, the person starts breathing normally and showing signs of life (moving, opening their eyes), or you become physically unable to continue and no one else is available to take over. There is no set time limit for bystander CPR. People have been successfully resuscitated after prolonged efforts, so persistence matters.
If an AED (automated external defibrillator) is available nearby, have someone retrieve it while you continue compressions. The device will give you voice prompts and will only deliver a shock if the heart rhythm calls for one. Resume compressions immediately after any shock.
Legal Protections for Bystanders
Every U.S. state has some form of Good Samaritan law that protects people who provide emergency care in good faith. These laws exist specifically to encourage bystanders to act. If you crack someone’s ribs during CPR, which is common and sometimes unavoidable, you’re protected from liability. The laws cover ordinary mistakes that a reasonable person might make while trying to help. They don’t protect against reckless or intentional harm, but performing CPR on someone in cardiac arrest is exactly the kind of action these statutes are designed to shield.
Good Samaritan laws won’t prevent someone from filing a lawsuit, but they provide a strong legal defense if that happens. In practice, lawsuits against bystanders who performed CPR are extraordinarily rare.