 We explain how to save lives with CPR. This is Maria. Her friend Peter has collapsed, and his heart has stopped. Maria is shocked. She has called an ambulance, but what can she do in the meantime? Maria has seen heroes save people in the movies, but how does it work? If the heart stops and the brain doesn't receive oxygenated blood, there's danger of brain damage. Cardiopulmonary resuscitation is an emergency procedure for keeping oxygenated blood flowing around a victim's body. Cardio means heart in Latin, and pulmonary involves lungs. Unlike in films, it isn't intended to restart somebody's heart. That usually requires an electric shock from paramedics. CPR involves repeatedly compressing the chest by about five centimeters at a rate of around 100 beats per minute in order to replace the heart's rhythm. Maria could also breathe into Peter's mouth or nose, though this isn't as important unless you're a trained professional. But there are some complications for Maria to keep in mind. Tearing of the liver can occur, as can bruising of the lungs. Rib fractures are relatively likely, but much better than the alternative. Without CPR, Peter would likely die. Maria is relieved that she now knows what to do and can increase Peter's chances of being revived. The ambulance arrives quickly and successfully saves his life, thanks to Maria's efforts. With CPR, you don't need to be a hero to save lives.