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A Guide to Understanding Parts of an AED

Automated external defibrillators (AEDs) are essential, life-saving devices used to restore a normal heart rhythm during sudden cardiac arrest. Their effectiveness hinges not only on user readiness but also on the proper function of each internal component.

For biomedical engineers, HTM professionals, emergency responders, and healthcare facility managers, understanding the parts of a defibrillator is key to ensuring uptime, preventing failure, and optimizing maintenance. This guide breaks down the major parts of an AED, how they work, and how you can maintain them to support consistent performance when every second counts.

Key Components of a Defibrillator and Their Functions

 

Power Supply

The power supply is what enables an AED to deliver a life-saving shock. Most portable AEDs are battery-operated, using lithium or rechargeable batteries. These require periodic replacement or charging to ensure sufficient energy storage.

A drained battery is one of the most common causes of AED failure. Biomedical professionals are encouraged to proactively monitor battery status and maintain a backup supply for each unit. You can source reliable replacement batteries from PartsSource’s full catalog of AEDs and parts.

Electrodes (Pads)

Electrodes are adhesive pads placed on the patient’s chest that deliver the electric shock. They’re coated with a conductive gel that can dry out over time, so checking expiration dates is critical. AED pads must be sealed, unexpired, and intact to function effectively.

Stocking both adult and pediatric pads ensures your AED is ready for patients of any age. Replacement electrodes are available through PartsSource’s selection of defibrillators and AED accessories.

Capacitor

The capacitor stores and rapidly discharges the electrical energy needed to restart the heart. It must be precisely calibrated, and malfunctions here can lead to ineffective shocks. While the component is internal and not typically replaced by end users, knowing its function is important for troubleshooting or diagnostics during servicing.

Charging Circuit

This component converts battery or outlet power into a high-voltage charge that feeds the capacitor. A faulty charging circuit can result in delays between shocks or failed charges altogether. For HTM professionals, this is one of the areas to test during annual defibrillator performance evaluations.

Control Panel

The control panel allows users to operate the external defibrillators, adjust settings, and initiate shock delivery. This interface varies by model and can include physical buttons, dials, or touchscreens. Ensuring these controls are functional and clearly labeled is part of routine AED maintenance, especially in high-use environments like emergency departments.

Display Screen

The screen displays the heart rhythm, battery level, prompts, and error messages. In public access AEDs, this screen provides step-by-step guidance for untrained users. Technicians should regularly confirm screen visibility, clarity, and responsiveness during checks.

Audio and Visual Prompts

Many AEDs provide voice instructions and visual indicators to guide the user through CPR and defibrillation steps. Malfunctioning audio can hinder an emergency response, particularly for non-clinical users. Firmware updates may occasionally enhance these features, so keeping software current is essential.

ECG Leads (For Advanced Defibrillators)

In clinical and EMS settings, advanced defibrillators include ECG leads to provide real-time rhythm monitoring. These leads help providers determine whether a shock is appropriate. Damage to cables or lead connectors can result in false readings or failed rhythm detection.

Software and Firmware

The software is responsible for rhythm analysis, shock decision-making, and overall device logic. Regular firmware updates from the manufacturer can address bugs, enhance decision algorithms, and comply with evolving regulatory standards. Many organizations schedule software audits alongside annual physical inspections.

Housing and Protective Case

The exterior case shields the internal components from dust, moisture, and mechanical stress. AEDs are often stored in wall-mounted cabinets or transport bags, and maintaining the integrity of both is vital. Cracks, corrosion, or worn seals can expose the device to damaging environmental conditions.

Why Understanding Defibrillator Parts Matters

For healthcare professionals, especially those in biomedical engineering and HTM, understanding the parts of an AED and defibrillator malfunction symptoms supports better troubleshooting, faster repairs, and improved regulatory compliance. Familiarity with each component allows teams to proactively:

  • Identify common failure points like expired batteries or electrode gel degradation.

  • Plan preventive maintenance aligned with manufacturer recommendations.

  • Extend device lifespan and maintain readiness in high-stakes scenarios.

Accurate knowledge also reduces downtime and supports mission-critical equipment uptime—a core driver of safer, more efficient patient care.

How PartsSource Supports AED Maintenance

At PartsSource, we provide biomedical and clinical teams with fast, reliable access to the parts they need to keep AEDs fully functional. Whether you’re replacing electrode pads, updating firmware, or managing a fleet of devices across multiple sites, our solutions are built to support consistent AED readiness.

  • Wide selection of OEM and high-quality aftermarket parts, including batteries, electrode pads, and accessories.

  • Fast shipping to reduce equipment downtime and support urgent replacements.

  • Access to medical equipment repair service to help diagnose, service, or restore AEDs that fail testing.

  • Support for centralized management of biomedical equipment, including service tracking, documentation, and compliance.

Our technology-enabled solutions are purpose-built to help you control maintenance workflows, standardize parts ordering, and ensure AEDs are always ready for use.

Conclusion

Understanding the parts of a defibrillator—from the capacitor and power supply to electrode pads and ECG leads—is essential for those responsible for keeping these life-saving devices functional.

Regular testing, proactive replacement of time-sensitive components, and software updates all contribute to equipment reliability in critical moments. For professionals managing AED programs across hospitals, EMS fleets, or large facilities, working with the right partner can make all the difference.

PartsSource supports AED readiness by providing access to AEDs and parts, expert service options, and streamlined inventory management. Explore our complete range of defibrillators and accessories to keep your biomedical equipment up and running—because ensuring healthcare is Always On™ starts with dependable devices and the people who maintain them.