A cycle in CPR is one set of 30 chest compressions followed by 2 rescue breaths. This 30:2 pattern is the standard for adults, and completing five cycles takes roughly two minutes. That two-minute block is the basic unit of time in CPR, after which rescuers reassess the person’s heart rhythm and, if needed, switch roles to stay fresh.
What One Cycle Looks Like
Each cycle starts with 30 chest compressions delivered at a rate of 100 to 120 per minute, pushing the chest down at least 2 inches (5 centimeters) on an adult. You let the chest fully recoil between each push, then pause briefly to give 2 rescue breaths. Each breath lasts about 1 second and uses just enough air to make the chest visibly rise. The pair of breaths should take no more than 5 seconds total so you can get back to compressions quickly.
Speed matters here because every compression builds up blood pressure inside the heart. That pressure, called coronary perfusion pressure, is what actually pushes blood to the brain and other organs. It climbs with each compression but drops the moment you stop pushing. Long pauses for breaths or fumbling with positioning erase the pressure you just built, so the cycle is designed to maximize time on the chest while still delivering oxygen.
Five Cycles, Two Minutes, Then Reassess
Five complete cycles of 30:2 take approximately two minutes at the recommended compression rate. At that mark, rescuers check whether the person’s heart has restarted or whether an automated defibrillator advises a shock. A simulator study of 119 physician teams found that counting five cycles produced more consistent timing than asking rescuers to estimate two minutes on a clock. Teams told to count cycles had less variation and better adherence to the target window.
If two rescuers are available, they should swap positions at this two-minute mark. Compression quality drops as fatigue sets in, often before the rescuer even feels tired. Research in Emergency Medicine International found that rotating every one minute actually improved compression depth and consistency compared to the standard two-minute swap, so switching sooner is fine if a second person is ready.
How the Cycle Changes for Children and Infants
For a single rescuer performing CPR on a child or infant, the cycle stays at 30 compressions and 2 breaths. The difference shows up when a second rescuer arrives. Two-rescuer pediatric CPR uses a 15:2 ratio, meaning 15 compressions followed by 2 breaths. The shorter cycle reflects the fact that cardiac arrest in children is more often caused by breathing problems than by heart rhythm issues, so delivering breaths more frequently is more important.
Compression depth also scales down. For infants and children, the target is at least one-third the depth of the chest from front to back, rather than the fixed 2-inch minimum used for adults.
When You Skip the Breath Portion
Hands-only CPR removes the breath component entirely, turning the “cycle” into continuous, uninterrupted compressions at 100 to 120 per minute. The American Heart Association encourages this approach for bystanders who witness an adult suddenly collapse. Research shows that bystanders are more likely to start CPR when they don’t have to perform mouth-to-mouth breathing. Reluctance to give rescue breaths, fear of doing something wrong, and lack of training are the most common reasons people hesitate.
Continuous compressions also deliver substantially more pushes per minute than the traditional cycle, since there’s no pause for breaths. For an adult who collapsed from a heart problem (the most common scenario), the blood still carries enough residual oxygen for the first several minutes that compressions alone can keep it circulating effectively. For drowning, choking, or pediatric arrests where oxygen depletion is the core issue, the full 30:2 cycle with rescue breaths remains the better approach.
Why Compression Quality Matters More Than Counting
Knowing the structure of a cycle is useful, but the quality of each compression within that cycle determines whether CPR actually works. Four factors define high-quality compressions: pushing hard enough (at least 2 inches deep on an adult), pushing fast enough (100 to 120 per minute), allowing the chest to come all the way back up between pushes, and minimizing any interruptions. Overventilating, where you breathe too hard or too many times, increases pressure inside the chest and can actually reduce the blood flow your compressions are trying to create.
If you’re the only rescuer and you lose count of compressions mid-cycle, don’t stop to think about it. Estimate and keep going. A slightly imprecise ratio delivered without long pauses is far more effective than perfect counting with 10-second gaps while you reset.