Cardiopulmonary resuscitation (CPR) is a life-saving technique used during cardiac arrest, when the heart suddenly stops beating. CPR helps by manually pumping the heart through chest compressions, which maintains blood flow to the brain and vital organs until professional help arrives or the heart can be restarted. Without CPR, brain damage can begin within 4–6 minutes due to lack of oxygen. Early CPR, especially combined with defibrillation, doubles or triples survival chances. Even hands-only CPR (without breaths) can be effective for untrained bystanders. Immediate action is critical—CPR buys time and helps keep the person alive.