Can electric shocks restart the heart?

The steady beep of a patient’s heart monitor is suddenly replaced by a steady tone – the patient has “flatlined” and his heart has stopped beating. “Clear!” yells the doctor as he charges the defibrillator and applies a shock to the patient’s chest. After a few tense moments, the flat line on the monitor begins tracing an up-and-down cycle – his heart has been restarted!

This familiar scene in movies and TV medical dramas is impossible in reality, because a heart that has stopped beating cannot be restarted with an electric shock.

Heartbeats are generated by cardiac muscle tissue. 99% of this tissue is made up of cardiomyocytes, which contract easily. 1% are pacemaker cells that regulate the heart contractions. The pacemaker cells create an electrical differential between the inside and outside of each cell. This is accomplished through chemical reactions involving sodium, potassium and calcium.

In a “flatlining” patient, the heart muscle has stopped responding to signals to contract. No amount of electric shock can reverse this serious situation, and in fact it can cause further harm. The appropriate treatment in such cases is CPR and a large dose of adrenaline.

In what medical situations are defibrillators actually used? When the heartbeat becomes erratic or inefficient. If applied quickly enough, electric shocks can be effective in restoring a more normal heart rhythm.

Bonus Fact: Heart monitors, if properly connected, never show a completely flat line, even if there is no pulse, or electrical activity in the heart.