CPR keeps blood moving to the brain and heart when someone's heart stops beating suddenly. The core response is: call emergency services first, then push hard and fast in the center of the chest — about 100 to 120 times a minute — until help or a defibrillator arrives. This guide walks through recognizing cardiac arrest and performing compressions step by step, based on guidance from the American Heart Association, the U.S. National Heart, Lung, and Blood Institute, and St John Ambulance.
Cardiac arrest happens when the heart's electrical system malfunctions and the heart stops pumping blood effectively. Without immediate action, a person loses consciousness within seconds and can die within minutes. The steps below summarize official first-aid guidance; they are not a substitute for a hands-on CPR certification course.
Recognizing a Cardiac Emergency
According to the U.S. National Heart, Lung, and Blood Institute (NHLBI), a person in cardiac arrest will collapse suddenly, lose consciousness, show absent or only gasping breathing, not respond to shouting or shaking, and have no detectable pulse. The NHLBI notes that rescuers do not need to locate a pulse before starting compressions — the priority is calling for help and beginning CPR.
St John Ambulance, the UK first-aid charity, advises checking for normal breathing by looking, listening and feeling for up to 10 seconds, and warns that occasional irregular gasps in the early stages of cardiac arrest should be ignored rather than mistaken for normal breathing.
The NHLBI distinguishes cardiac arrest from a heart attack: a heart attack is caused by a blocked artery that damages heart muscle but usually leaves the heart beating, while cardiac arrest is an electrical malfunction that stops the heartbeat outright and is fatal without rapid intervention. The institute adds that people who seek medical care for warning signs before a cardiac arrest are five times more likely to survive it.
Heart Attack vs. Cardiac Arrest (NHLBI)
Feature
Heart Attack
Cardiac Arrest
Underlying problem
Blocked artery in the heart
Electrical malfunction stopping the heartbeat
Does the heart keep beating?
Usually yes, though muscle is damaged
No
Possible warning signs
Chest pain more common in men
Shortness of breath more common in women; also fatigue, palpitations, dizziness
Immediate action
Call emergency services
Call emergency services and begin CPR
Step-by-Step: What To Do
Make sure the scene is safe, then check if the person responds — shake their shoulders and ask loudly if they are okay, St John Ambulance advises.
If there is no response, shout for help and call your local emergency number (or have someone else call) immediately.
Open the airway by tilting the head back and lifting the chin, then look, listen and feel for normal breathing for up to 10 seconds, per St John Ambulance guidance. Ignore occasional gasping.
If the person is not breathing normally, kneel beside them and place the heel of one hand on the center of the chest, with the other hand on top and fingers interlocked.
Keep your arms straight and shoulders directly over your hands, then push down to a depth of about 5–6 cm before letting the chest rise back up fully, St John Ambulance instructs.
Push at a rate of 100 to 120 compressions per minute, pressing hard and fast with minimal interruption.
If you are trained and willing, give two rescue breaths after every 30 compressions (a 30:2 ratio): tilt the head, pinch the nose, seal your mouth over theirs, and blow for about one second until the chest rises.
If you are untrained or unwilling to give breaths, continue hands-only chest compressions without stopping.
If a helper can locate an automated external defibrillator (AED), keep performing compressions while it is brought and attached, per St John Ambulance guidance.
Keep going until the person shows signs of life, professional help takes over, you are too exhausted to continue, or a defibrillator is ready to analyze the heart rhythm.
Hands-Only CPR vs. CPR With Breaths
The American Heart Association (AHA) promotes Hands-Only CPR — compressions without rescue breaths — as an option for bystanders responding to a teen or adult who suddenly collapses outside a hospital, particularly when the rescuer is untrained or unwilling to give breaths. St John Ambulance's guidance aligns with this: if you cannot or do not want to give rescue breaths, continuous compressions are still recommended rather than stopping CPR altogether.
CPR, especially if performed immediately, can double or even triple a cardiac arrest victim's chance of survival.
— American Heart Association
Why Minutes Matter
The AHA estimates that about 350,000 people in the United States experience cardiac arrest outside a hospital each year, and that it is fatal roughly 90% of the time. The association also states that only about 41% of adults who suffer cardiac arrest outside a hospital receive bystander CPR before emergency medical services arrive — a gap that immediate action from someone nearby can help close.
What Changed in the 2025 AHA Guidelines
The American Heart Association published its first full revision of resuscitation guidelines since 2020 in October 2025, in its journal Circulation. Alongside CPR technique, the update includes, for the first time, public guidance on when to use naloxone for a suspected opioid overdose, and expanded instructions for choking: alternating five back blows with five abdominal thrusts for adults and children, or five back blows with five chest thrusts (no abdominal thrusts) for infants. The guidelines also note that children aged 12 and older can be taught to perform effective CPR and use a defibrillator.
None of the information above replaces hands-on training. Organizations such as the American Heart Association and St John Ambulance offer certified CPR and AED courses that include supervised practice.
Questions
What is the difference between a heart attack and cardiac arrest?
A heart attack is caused by a blocked artery that damages heart muscle while the heart usually keeps beating; cardiac arrest is an electrical malfunction that stops the heartbeat entirely and is fatal within minutes without intervention, according to the NHLBI.
Do I have to give rescue breaths to perform CPR?
No. The American Heart Association recommends Hands-Only CPR — compressions only, no breaths — for bystanders responding to a sudden collapse in an adult or teen, especially if the rescuer is untrained or unwilling to give breaths.
How fast and how deep should chest compressions be?
St John Ambulance advises pushing at a rate of 100 to 120 compressions per minute to a depth of about 5 to 6 centimeters, letting the chest fully rise between pushes.
Do I need to check for a pulse before starting CPR?
According to the NHLBI, rescuers do not need to locate a pulse before starting compressions; if the person is unresponsive and not breathing normally, you should call emergency services and begin CPR right away.
What if the person is not breathing but I only hear occasional gasping?
St John Ambulance advises ignoring occasional, irregular gasps, since these are common in the early stages of cardiac arrest and do not count as normal breathing — CPR should still be started.
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