CPR follows a straightforward sequence: check for responsiveness, call 911, then begin cycles of 30 chest compressions followed by 2 rescue breaths. Repeating this cycle until emergency services arrive keeps blood flowing to the brain and heart when someone’s heart has stopped. Knowing these steps matters: people who receive bystander CPR have a 28% greater chance of surviving cardiac arrest compared to those who don’t.
Check for Responsiveness and Call 911
Before touching anyone, make sure the scene is safe for you. Look for hazards like traffic, fire, or electrical dangers. Once you’re confident it’s safe, tap or gently shake the person and shout, “Are you OK?” If they don’t move, make noise, or respond in any way, they need help immediately.
Shout for someone nearby to call 911 and grab an automated external defibrillator (AED) if one is available. If you’re alone, make the call yourself, put your phone on speaker, and stay with the person. The 911 dispatcher can coach you through CPR in real time if you’re unsure of the steps. Quickly check whether the person is breathing normally. Occasional gasps are not normal breathing. If they’re unresponsive and not breathing (or only gasping), start CPR right away.
Chest Compressions: The Core of CPR
Lay the person flat on their back on a firm surface. Kneel beside their chest. Place the heel of one hand on the center of their chest, right on the breastbone, then place your other hand on top and interlace your fingers. Keep your arms straight and position your shoulders directly over your hands so your body weight does the work.
Push hard and fast. Compress the chest to a depth of about 2 to 2.5 inches (5 to 6 cm) at a rate of 100 to 120 compressions per minute. That’s roughly two compressions every second. A useful mental trick: push to the beat of “Stayin’ Alive” by the Bee Gees, which runs at about 104 beats per minute.
Two details are just as important as depth and speed. First, let the chest fully recoil between compressions. Leaning on the chest between pushes prevents the heart from refilling with blood. Second, minimize interruptions. Every pause in compressions means blood stops flowing to the brain. If you need to stop for rescue breaths, keep that break as short as possible.
How Compressions Keep Blood Flowing
When the heart stops pumping on its own, chest compressions physically squeeze blood out of the heart and into the arteries that supply the brain and other organs. In younger people with narrower chests, compressions work mostly by directly compressing the heart itself. In older adults or those with broader chests, compressions raise overall pressure inside the chest cavity, which pushes blood forward through the circulatory system. Either way, the result is the same: enough blood flow to buy time until a defibrillator or paramedics can restart the heart.
Rescue Breaths: 30 Compressions, Then 2 Breaths
After every 30 compressions, give 2 rescue breaths. To do this, first open the airway using the head-tilt, chin-lift technique: place one hand on the person’s forehead and gently tilt their head back, then use two fingers under the bony part of the chin to lift it upward. This moves the tongue away from the back of the throat and clears the airway. Studies show this technique successfully opens the airway in about 91% of unconscious patients.
Pinch the person’s nose shut, seal your mouth over theirs, and blow steadily for about one second. Watch for the chest to rise. If it does, deliver a second breath the same way. If the chest doesn’t rise, re-tilt the head and try again. Each breath delivers about 16% oxygen, which is enough to sustain vital organs. Don’t blow too hard or too many times. Overventilating pushes air into the stomach and can reduce blood flow.
Continue repeating cycles of 30 compressions and 2 breaths until the person starts breathing on their own, an AED becomes available, or emergency medical services take over.
Hands-Only CPR Is an Effective Alternative
If you’re untrained, uncomfortable with mouth-to-mouth contact, or simply unsure about rescue breaths, hands-only CPR (continuous chest compressions without breaths) is not just acceptable, it’s highly effective. A meta-analysis of three randomized trials found that 11.5% of people who received compression-only CPR from bystanders survived to hospital discharge, compared to 9.4% of those who received standard CPR with breaths. That’s a meaningful advantage, likely because bystanders who skip the breaths compress more consistently and interrupt compressions less often.
Hands-only CPR is recommended for untrained bystanders responding to an adult who suddenly collapses. It’s simpler to learn, easier for 911 dispatchers to coach over the phone, and people are significantly more willing to start it. In studies, bystanders told to perform standard CPR were more likely to withhold help entirely than those told to do compressions only. The best CPR is the CPR that actually gets started.
One caveat: for cardiac arrests that aren’t caused by a heart problem (drowning, drug overdose, choking, or any situation where breathing failed first), rescue breaths become more important because the person’s blood oxygen is already depleted.
CPR for Infants and Children
The basic sequence is the same for children and infants, but the technique changes to match their smaller bodies.
- Children (age 1 to puberty): Use one or two hands to compress the center of the chest to a depth of about 2 inches. Maintain the same 30:2 ratio of compressions to breaths.
- Infants (under age 1): Use just two fingers placed on the center of the chest, just below the nipple line. Compress to a depth of about 1.5 inches. The 30:2 ratio still applies.
Rescue breaths are especially important for infants and children. Pediatric cardiac arrests are more often caused by breathing problems than by heart rhythm issues, so maintaining oxygen delivery matters more than in adult cases. Cover both the infant’s mouth and nose with your mouth when giving breaths, and use gentle puffs rather than full breaths.
Using an AED
If someone brings an AED, use it as soon as possible. Turn it on and follow the voice prompts. The device will tell you exactly where to place the adhesive pads on the person’s bare chest. Once the pads are attached, the AED analyzes the heart rhythm automatically and determines whether a shock is needed. If it advises a shock, make sure no one is touching the person, then press the shock button. Immediately resume CPR with chest compressions after the shock is delivered. The AED will prompt you to stop for another rhythm check every two minutes.
What to Expect Physically
Performing CPR is exhausting. Compressing a chest 100 to 120 times per minute at the correct depth takes real effort, and fatigue sets in quickly. Compression quality starts to drop after about two minutes. If another bystander is available, switch off every two minutes to keep compressions effective. Swap during the brief pause for breaths to minimize interruption.
You may hear or feel ribs crack during compressions. This is common, particularly in older adults, and it does not mean you’re doing something wrong. Broken ribs heal. A stopped heart without CPR is fatal. Keep compressing.
On the legal side, Good Samaritan laws in every U.S. state protect bystanders who provide emergency CPR in good faith. These laws shield you from civil liability for ordinary mistakes, like a cracked rib, as long as you act voluntarily, don’t demand payment, and don’t act with reckless disregard for the person’s safety.
Quick Reference: The Full Sequence
- 1. Scene safety: Make sure the area is safe for you.
- 2. Check responsiveness: Tap, shake gently, shout “Are you OK?”
- 3. Call 911: Or direct someone else to call and get an AED.
- 4. Check breathing: No breathing or only gasping means start CPR.
- 5. Begin compressions: 30 compressions, 2 to 2.5 inches deep, 100 to 120 per minute.
- 6. Give 2 breaths: Tilt head back, lift chin, blow for 1 second each. (Skip if untrained.)
- 7. Repeat: Continue 30:2 cycles without stopping.
- 8. Use an AED: As soon as one arrives, follow its prompts.
- 9. Keep going: Don’t stop until the person recovers, paramedics arrive, or you’re physically unable to continue.