Cardiopulmonary resuscitation (CPR) is an emergency procedure used when a person's heart has stopped beating and breathing has stopped. It involves chest compressions and rescue breathing to maintain circulation and oxygenation until medical help arrives. Basic life support (BLS) involves chest compressions, opening the airway, and rescue breathing without any equipment other than a face mask or shield. BLS aims to maintain circulation and oxygenation through chest compressions and rescue breathing until advanced life support can take over. Proper CPR technique is critical to maximize its effectiveness in saving lives.