You know (from watching TV, most likely) that when a patient is in cardiac arrest the defibrillator is going to come out. And if you believe what you see in your favorite TV emergency room, it's quite a dramatic survival tool for saving flatlining patients. Paddles are rubbed together, someone yells "CLEAR!" and then one big shock is delivered to the patient's chest. He jerks, probably violently, and then you hear the sound that's always music to the entire fictional ER team's ears: the beeping of the heartbeat on the heart monitor.
But defibrillators don't work that way. In reality, a defibrillator sends an electric shock to a heart to reset a rapid or uncoordinated heart rate. (The irregular contraction of heart muscle fibers that causes this condition is called fibrillation, thus the name of the device). It can't restart a heart once it's stopped beating, though. And rubbing those pads together? Only if you want to void the warranty on the equipment. It can permanently damage the device.