A young woman is experiencing chest pains. She calls 911, but collapses just as the operator answers.
Paramedics arrive and do an assessment–checking her airway, cutting off clothing and starting an IV. She has no pulse. They start CPR. Then start with a resuscitator, then switch to mouth to mouth. Later, they use defibrillation to finally revive her.
At the hospital, she is weak but stable. They leave her to rest. Soon, she goes into arrest, her pulse racing, then flatlines. They quickly start CPR and switch to defibrillation then back to CPR over and over.