On television, CPR revives patients about 75 percent of the time. In reality, survival after an adult cardiac arrest outside a hospital is closer to 10 percent. This episode explains what happens when the heart stops: brain damage begins in about four minutes and becomes irreversible after about seven. Chest compressions rarely restart the heart. Their purpose is to keep some oxygenated blood moving to the brain and heart until help arrives, at 100 to 120 compressions per minute with full recoil so the chambers can refill.

It took a long time to get here. In the 19th century the Silvester technique raised and lowered a patient’s arms to work the lungs, and Holger Nielsen later pressed on the back of a patient lying face down. In the 1960s James Jude, Guy Knickerbocker, and Peter Safar combined chest compressions with mouth-to-mouth. In 2010 the American Heart Association changed ABC to CAB, and hands-only CPR is now recommended for bystanders when an adult collapses. The episode explains why children, drowning victims, and overdose victims still need rescue breaths, and why a defibrillator resets ventricular fibrillation but is never used on a flat line.

• Why a suddenly collapsed adult still has oxygen-rich blood waiting to be circulated
• Compressions five to six centimeters deep and why broken ribs are common
• Stayin’ Alive at 104 beats per minute and Another One Bites the Dust at 110
• Bystander AED use raising survival to around 35 percent
• Animal trials of cardioplegic blood infusion after more than 70 minutes of arrest