If someone near you goes into cardiac arrest, you need to act within seconds. Call 911 (or have someone else call), start chest compressions immediately, and use an AED if one is available. The heart has stopped pumping blood effectively, and every minute without action reduces the chance of survival. People who receive bystander CPR before paramedics arrive survive at significantly higher rates than those who don’t.
Recognizing Cardiac Arrest
Cardiac arrest looks different from what most people expect. The person will suddenly collapse, become unresponsive, and either stop breathing entirely or produce occasional gasping breaths. Those gasps, called agonal breathing, appear in up to 40% of cardiac arrests and are frequently mistaken for normal breathing. This confusion causes many bystanders to hold off on CPR when they should be starting it. If someone is unresponsive and not breathing normally, treat it as cardiac arrest.
Cardiac arrest is not the same as a heart attack. A heart attack is a blockage problem: blood flow to part of the heart muscle gets cut off, usually by a clot. The person is typically conscious and may feel chest pressure, arm pain, nausea, or shortness of breath. Cardiac arrest is an electrical problem: the heart’s rhythm malfunctions and it stops pumping blood altogether. The person loses consciousness within seconds. A heart attack can trigger cardiac arrest, but they require very different responses. A heart attack needs medical treatment. Cardiac arrest needs CPR right now.
Step 1: Call 911 and Start Compressions
Check for responsiveness by tapping the person’s shoulders and shouting at them. If they don’t respond and aren’t breathing normally, call 911 immediately. If someone else is nearby, have them call while you begin CPR. If you’re alone, put your phone on speaker, call 911, and start compressions. The dispatcher can walk you through the process in real time if you’re unsure what to do.
Place the heel of one hand on the center of the person’s chest, between the nipples. Stack your other hand on top and interlock your fingers. Keep your arms straight with your shoulders directly above your hands, and push hard and fast. The target depth is at least 2 inches, and the target rate is 100 to 120 compressions per minute. That’s roughly the tempo of the song “Stayin’ Alive.” Let the chest come all the way back up between each compression. This recoil is what allows the heart to refill with blood.
Two inches of compression depth sounds aggressive, and it is. Effective CPR requires real force. You may feel ribs crack, and that’s normal. A cracked rib heals. A stopped heart without CPR does not.
Hands-Only CPR vs. Rescue Breathing
For most bystanders, hands-only CPR (compressions without mouth-to-mouth) is the recommended approach. Research published in the New England Journal of Medicine found that chest compressions alone produced comparable or better survival rates than traditional CPR with rescue breathing for adults whose arrest had a cardiac cause. Among patients with the most common treatable rhythm, survival was 31.9% with compressions alone versus 25.7% with compressions plus rescue breaths.
The exception is cardiac arrest caused by drowning, choking, or suffocation. In these cases, the underlying problem is a lack of oxygen rather than an electrical malfunction, and rescue breaths become more important. If you’re trained in full CPR and the arrest appears to have a respiratory cause, alternate 30 compressions with 2 rescue breaths. If you’re not trained or not sure what caused the arrest, continuous chest compressions are your best option.
Step 2: Use an AED
An automated external defibrillator (AED) is the single most effective tool for restarting a heart in cardiac arrest. These devices are found in airports, gyms, offices, schools, and many other public spaces. If one is nearby, send someone to grab it while you continue compressions. If you’re alone, don’t stop CPR to search for one unless you know exactly where it is and can retrieve it within a minute or two.
AEDs are designed to be used by people with zero training. When you open the lid, the device powers on (sometimes automatically) and gives you spoken, step-by-step instructions. Here’s what to expect:
- Expose the chest. Remove or cut away any clothing covering the person’s chest. Wipe the skin dry if it’s wet.
- Attach the pads. Peel the backing off the two adhesive pads and place them exactly where the diagrams on the pads show, typically one on the upper right chest and one on the lower left side.
- Let the AED analyze. The device will tell everyone to stand clear while it checks the heart rhythm. Do not touch the person during this step.
- Deliver a shock if prompted. The AED will only advise a shock if it detects a rhythm that can be corrected. Press the button when instructed. If no shock is advised, resume CPR immediately.
For children over 8 years old or weighing more than 55 pounds, use the standard adult pads. Some AEDs come with smaller pediatric pads for younger children. After any shock is delivered, resume chest compressions right away. The AED will prompt you to pause again after two minutes for another rhythm check.
CPR for Infants and Small Children
The principles are the same for children and infants, but the technique changes. For children ages 1 to 8, use one hand instead of two for compressions. For infants under 1 year, use two fingers placed on the breastbone just below the nipple line. In both cases, compress to a depth of about one-third the chest’s front-to-back diameter, which works out to roughly 1.5 inches for infants and 2 inches for children.
Because cardiac arrest in children is more often caused by a breathing problem than an electrical one, rescue breaths are more important here than for adults. If you’re trained, give 2 gentle breaths after every 30 compressions. Cover both the mouth and nose of an infant when delivering breaths.
What Happens While You Wait for EMS
CPR is exhausting. If another bystander is available, switch off every two minutes to keep compression quality high. Fatigue causes people to compress too shallowly without realizing it, and shallow compressions don’t move enough blood. When switching, minimize the pause to under 10 seconds.
Continue CPR until one of three things happens: emergency medical services arrive and take over, the person starts breathing normally and becomes responsive, or an AED delivers a shock and the person regains consciousness. Do not stop compressions just because you’re tired or unsure if it’s working. Even CPR that feels inadequate is better than no CPR at all.
A large study of out-of-hospital cardiac arrests found that 17.6% of people who received bystander CPR regained a pulse, compared to 12.0% of those who received no bystander CPR. Those numbers may seem modest, but they represent a nearly 50% relative improvement in the odds of the heart restarting before paramedics arrive.
Legal Protections for Bystanders
Every U.S. state has a Good Samaritan law that shields people who provide emergency care in good faith. These laws generally protect any person who voluntarily attempts to help at the scene of an emergency, without expecting payment, from being held liable for civil damages. The only exception in most states is gross negligence or intentional harm. Performing CPR on someone in cardiac arrest, even imperfectly, falls squarely within the protection these laws were written to provide.
The legal risk of stepping in is essentially zero. The risk of doing nothing is a person’s death. Bystander hesitation remains one of the biggest barriers to survival in out-of-hospital cardiac arrest, and fear of legal consequences is a common reason people give for not acting. That fear is unfounded.