Defibrillators are devices that save lives by restoring the heart to its normal sinus rhythm in cases of critical cardiac anomalies such as asystole or fibrillation. They achieve this by delivering a short but high-capacity current through the patient.

Defibrillators can boost energy from their batteries to up to 360J within seconds using step-up circuits. In terms of electrical transmission, defibrillators are categorized into two types: monophasic and biphasic. Monophasic defibrillators transmit current in a single direction during the positive phase, while biphasic defibrillators send current in both the positive and negative phases, meaning bidirectionally. A critical point here is that the current must be sent asynchronously with the T-wave to avoid causing ventricular fibrillation. Today, most defibrillators achieve this using an EKG-based algorithm called Cardioversion.

Another increasingly common type of defibrillator is the AED (Automated External Defibrillator). AEDs are automatic defibrillators located primarily in public areas such as factories, schools, museums, universities, offices, and government buildings—places with high human traffic and population. AEDs are designed to operate with minimal user responsibility when needed.

Once activated, an AED guides the user through the process with audible and visual instructions, resolving the situation by delivering a predefined current to the patient via pads, suitable for both pediatric and adult patients. AEDs initially perform a rapid EKG analysis to determine whether the patient needs a shock, then deliver the shock accordingly. These semi-autonomous AEDs are critical barriers preventing potential deaths or permanent brain damage.