Chest compressions are rhythmic pushes applied to the center of a person’s chest during cardiac arrest, manually pumping blood through the body when the heart has stopped beating on its own. They are the core technique of CPR (cardiopulmonary resuscitation) and the single most important action a bystander can take to keep someone alive until emergency medical help arrives. People who receive bystander CPR have a 28% greater chance of surviving cardiac arrest compared to those who don’t, according to data from the National Institutes of Health.
How Compressions Keep Blood Flowing
When the heart stops, blood flow to the brain and other organs ceases within seconds. Brain cells begin dying after roughly four to six minutes without oxygen. Chest compressions create an artificial version of the heartbeat by physically squeezing the heart between the breastbone and the spine, forcing blood out into the arteries with each push.
Scientists have debated exactly how this works. The leading explanation, called the cardiac pump theory, holds that compressing the chest directly squeezes the heart’s chambers, pushing blood forward much like a normal heartbeat would. Imaging studies performed during actual CPR have confirmed this: the heart’s chambers shrink during each compression and refill when the chest is released. That release phase matters just as much as the push itself, because it creates a slight vacuum that draws blood back into the heart, reloading it for the next compression. Leaning on the chest between pushes prevents this refilling and dramatically reduces blood flow.
The Correct Technique for Adults
The American Heart Association recommends compressing an adult’s chest at a rate of 100 to 120 compressions per minute, which roughly matches the tempo of the song “Stayin’ Alive.” Each compression should push the chest down at least 2 inches (5 centimeters). You place the heel of one hand on the center of the chest, between the nipples, stack your other hand on top, lock your elbows, and push straight down using your body weight rather than arm strength alone.
Allowing the chest to fully spring back up between each push is critical. Equally important is minimizing pauses. Every second you stop compressing, blood pressure drops to nearly zero and the brain loses oxygen again. If you’re alone, keep compressing continuously until help arrives or someone can take over.
Why Rescuers Tire Quickly
Compression quality deteriorates faster than most people realize. In a study measuring rescuer performance over time, the percentage of compressions meeting quality standards dropped from 94% to less than 75% within just two minutes, and continued falling to 32% by the ten-minute mark. Rescuers often don’t feel fatigued yet at the two-minute point, but the depth and consistency of their compressions are already declining. This is why guidelines recommend switching with another rescuer every two minutes if possible. If you’re performing CPR with someone else nearby, trading off frequently produces far better results than one person pushing through exhaustion.
Hands-Only CPR for Bystanders
If you witness an adult suddenly collapse, hands-only CPR (compressions without rescue breaths) is the recommended approach for untrained bystanders. The American Heart Association has confirmed that hands-only CPR is as effective as traditional CPR with mouth-to-mouth breathing during the first several minutes of an adult’s cardiac arrest. The person’s blood still contains enough oxygen to sustain organs for a short window, so keeping that blood circulating with compressions is what matters most.
There are important exceptions. Infants, children, drowning victims, and people who collapse from drug overdose or breathing problems need both compressions and rescue breaths, because their cardiac arrest is typically caused by a lack of oxygen rather than a heart rhythm problem. In these cases, the blood’s oxygen supply is already depleted, and compressions alone won’t deliver what the brain needs.
Differences for Infants and Children
Smaller bodies require adjusted techniques. For infants, the 2025 AHA guidelines recommend either a one-hand technique or a two-thumb method where the rescuer wraps both hands around the infant’s torso and compresses with the thumbs. The older approach of using two fingertips on the breastbone has been dropped from guidelines because it doesn’t achieve adequate depth.
For children aged one to eight, using two hands produces deeper, more effective compressions than one hand. The target depth for children is about one-third the depth of the chest from front to back. Research on pediatric cardiac arrest has found that achieving compression depths of at least 2 inches (5 centimeters) in children is associated with improved rates of return of a pulse and 24-hour survival. The compression rate stays the same as for adults: 100 to 120 per minute.
Injuries From Compressions
Effective chest compressions require significant force, and that force can cause injury. A study using full-body CT scans of cardiac arrest survivors found that 74% had rib fractures and 18% had a sternal (breastbone) fracture after resuscitation. Mechanical CPR devices, which automate compressions, were associated with even higher fracture rates: 36% sternal fractures compared to 12% with manual compressions.
These numbers can seem alarming, but they reflect reality: the compressions were strong enough to circulate blood and keep the person alive. A broken rib heals. Cardiac arrest without compressions is fatal in the vast majority of cases. Worrying about causing rib fractures is one of the most common reasons bystanders hesitate, but the trade-off is not close. Cracked ribs are an expected side effect of compressions done well, not a sign that something went wrong.
What Researchers Still Don’t Know
Despite decades of CPR guidelines, the optimal compression depth, rate, and timing are still not fully settled. The 2025 AHA guidelines explicitly identify the ideal compression metrics for both adults and children as a top research priority. Current recommendations are based on the best available evidence, but the “perfect” compression likely varies by body size, age, and the cause of the arrest. What is clear is that compressions within the recommended range of 100 to 120 per minute and at least 2 inches deep are dramatically better than no compressions at all, and that starting immediately is more important than performing them perfectly.