A defibrillator treats a dangerous rhythm—not a stopped heart
A defibrillator delivers a brief electrical shock to the heart. Its main purpose is to treat certain chaotic rhythms, especially ventricular fibrillation, in which the heart’s lower chambers twitch in disorganized bursts instead of pumping blood. The shock interrupts that electrical chaos, giving the heart’s own rhythm-making system a chance to take control again.
That is why a shock can help when a person’s heart is quivering rather than pumping. It does not mechanically squeeze the heart or supply it with a new beat on command.
Why the movie “flatline” shock is misleading
A flatline usually means there is no detectable electrical activity in the heart. A shock is not the standard treatment for that rhythm: it cannot jolt an electrically inactive heart back into action. Responders instead use CPR to keep some blood moving, give appropriate medicines, and look for causes they can treat.
This distinction matters because “cardiac arrest” describes the emergency—blood is no longer circulating effectively—not one specific heart rhythm. Some arrests involve rhythms that can respond to a shock; others do not. A heart attack, meanwhile, is a blockage of blood flow to heart muscle. It can trigger cardiac arrest, but the two terms do not mean the same thing.
What happens after the shock
Even when a shock is appropriate, it may not restore an effective heartbeat immediately. CPR often continues, and an automated external defibrillator (AED) checks the rhythm and advises whether a shock is called for. The goal is to restore a rhythm that pumps blood, not simply to make the monitor display a heartbeat. That is why real resuscitation is a sequence of rhythm checks, shocks when indicated, and continued CPR—not one dramatic zap that brings someone straight back.
