Chest compression is the act of rhythmically pressing down on someone’s breastbone to manually pump blood through their body when their heart has stopped beating. It is the core technique of CPR (cardiopulmonary resuscitation) and the single most important action a bystander can take during cardiac arrest. Current guidelines call for pressing at least 2 inches deep into the chest at a rate of 100 to 120 pushes per minute.
How Compressions Keep Blood Moving
When the heart stops, blood flow to the brain and other organs drops to zero within seconds. Chest compressions act as a substitute heartbeat, generating enough pressure to push oxygenated blood out of the heart and into the body’s circulation. Two complementary mechanisms explain how this works.
The first is called the cardiac pump mechanism. When you push down on the breastbone, you physically squeeze the heart between the sternum and the spine. This forces the heart’s valves to open and close in a pattern similar to a normal heartbeat. On the downstroke, the valves leading to the body and lungs open, pushing blood out. When you release, those valves close and the filling valves open, allowing blood to flow back in.
The second mechanism involves the entire chest cavity. Pressing down raises the pressure inside the chest, which pushes blood out of all the blood vessels in the thorax, not just the heart itself. In this model the heart acts more like a passive tube that channels blood outward whenever chest pressure exceeds the pressure outside the chest. Current evidence suggests both mechanisms work together during real-world CPR, and performing high-quality compressions activates both.
Depth, Rate, and Recoil
Three variables determine whether compressions actually move enough blood to matter: how deep you push, how fast you push, and whether you let the chest fully spring back between pushes.
For adults, the American Heart Association recommends a depth of at least 2 inches (5 centimeters) and a rate of 100 to 120 compressions per minute. That pace is roughly the tempo of the song “Stayin’ Alive.” For children aged 1 to 8, the target is about one-third the depth of the chest, and for infants the same one-third guideline applies.
Full chest recoil between compressions is just as critical as the compression itself. When you completely lift your weight off the chest, the sternum springs back outward, creating negative pressure inside the chest cavity. That negative pressure acts like a vacuum, pulling blood from the veins back into the heart so it has something to pump on the next compression. Leaning on the chest between pushes, even slightly, reduces this refilling effect and lowers the amount of blood each compression delivers. Rescuers who are fatigued tend to lean without realizing it, which is why guidelines recommend switching with another rescuer every two minutes if possible.
Compressions With or Without Breaths
Traditional CPR alternates chest compressions with rescue breaths. Hands-only CPR skips the breaths entirely and uses continuous compressions. For bystanders responding to an adult who suddenly collapses, hands-only CPR is not just simpler but statistically more effective. A meta-analysis pooling data from randomized controlled trials found that 11.5% of patients who received compression-only CPR from bystanders survived to hospital discharge, compared with 9.4% of those who received standard CPR with breaths. That translates to about a 24% relative improvement in survival.
The likely explanation is time. Every pause for a breath means several seconds without compressions, and blood flow drops to near zero almost immediately when compressions stop. Untrained bystanders also tend to hesitate or delay CPR when they feel unsure about performing mouth-to-mouth, so removing that barrier gets compressions started sooner.
The 2025 AHA guidelines do note that adding breaths is recommended for rescuers who are willing and able, and it remains especially important for children. Pediatric cardiac arrest is more often caused by breathing problems rather than heart rhythm issues, so children benefit more from receiving both compressions and breaths. Compression-only CPR in children is still far better than doing nothing at all.
Technique Differences for Infants and Children
Performing compressions on a child or infant requires adjusting your technique to match a smaller body. For children aged 1 to 8, studies show that using two hands (the same position as for an adult, just scaled down) produces better compression depth than using one hand. For infants, the 2025 guidelines eliminated the old two-finger technique after evidence showed it rarely achieved adequate depth. The recommended approaches for infants are now the two-thumb encircling hands method, where you wrap both hands around the infant’s torso and compress with your thumbs, or a one-hand technique with the heel of one hand on the lower breastbone.
Research on pediatric chest anatomy confirms that compressing to one-third of the chest’s front-to-back diameter is safe and does not damage internal organs. In children treated in hospitals, achieving a compression depth of at least 2 inches for at least 60% of CPR improved rates of return of spontaneous circulation and 24-hour survival.
Common Injuries From Compressions
Effective chest compressions require significant force, and injuries to the chest wall are common. A large systematic review and meta-analysis found that 55% of patients who received CPR sustained rib fractures, and about 24% had a fracture of the sternum. In roughly 36% of cases, multiple adjacent ribs broke in a pattern that created a segment of the chest wall that moved independently (called a flail segment).
These numbers can sound alarming, but they reflect the reality that saving a life requires compressing hard enough to move blood. Broken ribs heal. A heart that never restarts does not. Guidelines emphasize that rescuers should not hold back on depth out of fear of causing fractures. The risk of injury is accepted because the alternative, no blood flow to the brain, is fatal within minutes.
Why Starting Quickly Matters Most
Brain cells begin dying roughly four to six minutes after blood flow stops. Every minute without compressions reduces the chance of survival by about 7 to 10 percent. The entire purpose of chest compressions is to buy time, keeping enough oxygen reaching the brain and heart until a defibrillator or emergency medical team can restore a normal heartbeat. Even imperfect compressions dramatically improve the odds compared with waiting and doing nothing. If someone collapses and is not breathing normally, placing the heel of your hand on the center of their chest and pushing hard and fast is the single most effective thing you can do.