Cardiopulmonary resuscitation (CPR) is a lifesaving technique used in emergencies when someone's breathing or heartbeat has stopped. It involves a combination of chest compressions and rescue breaths to help maintain blood flow and oxygen to vital organs until professional medical help arrives. CPR can be performed by bystanders and is crucial in cases of cardiac arrest or drowning. The procedure typically starts with calling for emergency assistance and checking the person's responsiveness. If unresponsive, the rescuer begins chest compressions at a rate of 100 to 120 compressions per minute, followed by rescue breaths if trained. Early CPR can significantly increase the chances of survival.