The way a defibrillator works with a stopped heart is by analysing, and it that way it does “help it beat again”. But it won’t shock a stopped heart. The name says it all; it de-fibrillates. The heart has to be fibrillating for it to be de-fibrillated; the shock can only correct an archaic rythmn, not the absence of rythmn.

If there’s no electric activity, the person needs meds like epinephrine, not a shock.

The thing with TV shows, is that they often show a flat line on an ECG monitor and then shock the patient, which is basically useless except at burning the patient’s skin and stopping effective compressions during CPR. The kind of ECG we should see during a shock is atrial fribrillation (a-fib) and ventricular fibrillation (v-fib). Those should have a very wavy ECG line.

Source: am nurse (edit: a better nurse corrected me on some differences between shocking for a defibrillation and for a cardioversion, go read their comment)

There are certain devices that do do that, but it’s not a defibrillator. A defibrillator will stop/prevent an arrhythmia by stopping the heart, and letting it restart on its own (hoping that it goes to a normal rhythm), and delivering further shocks if it gets back into one.

The device you’re looking for to help a heart beat again would be a pacer, or a pacemaker, which will shock the heart to force it to pump, and restore rhythm that way. They’re commonly used for conditions like heart failure, if the heartbeat generation systems/internal pacemaker can’t generate a heartbeat quickly enough to sustain life.