Electricity and the Heart

This article was inspired by an email we received from a viewer of our HVAC School YouTube channel, Jim Holbrook. Thank you, Jim!

Disclaimer: This article is written to help educate you and hopefully save lives. We are NOT an authority on the topic. OSHA, as well as company best practices and risk assessments, should be your guide. Proper CPR and first aid training usurps this guide and should be followed. 

If you work in the HVAC or refrigeration industry, you don’t need us to tell you that dangerous situations are commonplace. Electrocution is relatively uncommon, but it’s still a possibility that HVAC techs need to keep in mind. It may cause severe injury or death.

However, it doesn’t seem like many people talk about the core cause of death by electrocution. It takes relatively few amps to kill a human being because it disrupts the signals that your heart relies on to pump properly. 

In this article, we will discuss how the heart muscle works, how electrical shocks interact with the heart, and ways to avoid lethal electrocution or help victims.


The human heart: a rhythmic machine

The human circulatory system is a complex topic. It can take at least a couple of weeks for high school students to learn the ins and outs of it, so I’ll try to keep it as simple as possible.

The heart is a muscle that pumps blood to all the organs of your body. It has four chambers: two upper atria and two lower ventricles. The two upper chambers, called the right and left atria, receive and collect blood. The two lower chambers pump blood to parts of your body. (The right ventricle pumps low-oxygen blood to the lungs via the pulmonary artery. The left ventricle pumps high-oxygen blood to the whole body through the aorta and connected arteries.)

The blood moves through the heart in stages. A collection of blood will enter the heart in the right atrium and travel to the right ventricle. It exits the right ventricle via the pulmonary artery, where it goes to the lungs to collect oxygen. The oxygen-rich blood returns to the heart in the left atrium and travels to the left ventricle. It exits the left ventricle via the aorta and travels throughout the body via the arteries.

The heart pumps blood in three stages:

  1. The right and left atria contract in unison, pumping blood into the right and left ventricles.
  2. The ventricles contract in unison (called systole) to propel blood out of the heart.
  3. After the second stage, the heart muscle relaxes (called diastole) before the next heartbeat.


Our heart’s electrical impulses

The ventricles contract and relax in a rhythm. If you have ever received an electrocardiogram (EKG) at a medical facility, you probably saw a chart with jagged rhythmic lines. That chart shows your heart rhythm.

This relaxation is a critical moment in a heartbeat, which you can see on an EKG. The heart muscle relies on electrical signals to tell it when to pump after the relaxation. When the heart muscle relaxes, potassium ions in the heart muscle move or reset from one side of the heart muscle wall to the other in preparation for the next contraction of the chambers. 

Potassium is an electrolyte, meaning that it is a substance that conducts electricity as it dissociates into an ion (a charged atom). When potassium ions have been reset, they enter a ready state to facilitate pumping. When potassium ions move to the opposite side of the heart wall, they allow the electrical impulse to progress and the heart to pump.

If a current as little as seven milliamps (0.007 A) travels across the heart while the potassium ions are moving from one side of the heart muscle wall to the other, it will cause the heart muscle to quiver. This is also known as ventricular fibrillation. 

The electrical current interrupts the potassium ions’ movement. The ions become uncoordinated, not knowing where to go to restart the pumping cycle. Cardiac arrest and death happen within minutes, as the heart cannot pump blood in this state.

In short, electrocution is about timing. A victim may be hit by amperage across the heart and not go into ventricular fibrillation. It depends on the location of those potassium ions. (We should note that the victim still won’t be out of the woods if their heart doesn’t go into ventricular fibrillation. The current flow will still create heat, which burns bone and internal tissues. On top of that, they may develop other conditions that cause irregular heartbeats or arrhythmias.)


What can you do to help a victim?

Suppose one of your teammates has suffered an electric shock, and the potassium ions in his heart can no longer reset. What can you do to help him?

Your mind may go to three things: chest compressions, mouth-to-mouth, and defibrillation.

The victim can only be saved by defibrillating the heart with a high voltage that will get the potassium ions back in position for the next contraction of the heart muscle. CPR chest compressions and mouth-to-mouth will not do any good to save the victim because they don’t do anything to correct or reset the potassium ions.

You may be familiar with the paddles we see in dramatic emergency room scenes in movies and TV shows. Doctors use those paddles to deliver high-voltage shocks to ventricular fibrillation patients, and the shock resets the potassium ions. 

However, you usually only see the paddle-type defibrillators in medical settings. Automated External Defibrillators (AEDs) use sticky pads instead of paddles, and they are common in most private and public buildings where someone may need to automate the heart reset process. 

AED usage

Heaven forbid you’ll ever need to use an AED, but if that day ever comes, we’ve put together some information on what you need to do. (Sources include Mayo Clinic and EMS Safety Services.)

1. Power on the AED

Place the AED by the victim’s head and power it on. Some units will have a button that you need to press. Others will power on automatically once you lift the hood.

2. Attach the defibrillator pads

Most public AEDs use pads that stick to the patient’s chest and connect to the defibrillator. Wired paddles mostly exist in medical settings. 

Expose the victim’s chest. You may need to tear or remove their shirt and wipe any sweat or excess moisture from their skin. 

Normally, you apply the pads on the upper right side of the chest (just below the collarbone) and the lower left side of their chest. Keep in mind that you place these on the victim’s right and left sides, not your right and left. (Look at the image above for reference.)

In some cases, you will need to attach the pads to the defibrillator manually. Do that if it hasn’t already been done for you.

3. Make sure the victim is clear and shock them

The AED literally delivers an electrical shock. The high-voltage zap repositions the potassium ions so that they may move and facilitate pumping once again.

When you prepare to shock the victim, absolutely NOBODY should touch them or their clothes. Look around to make sure that everyone has stood back and is not at risk of shock.

When everybody has backed away from the victim (yourself included), loudly declare, “Everybody clear.”

Press the appropriate button on the unit to deliver a shock.


Most AED guides and medical education programs emphasize the importance of chest compressions after using the AED. While they are correct that chest compressions are important for heart attack victims, chest compressions won’t do anything for electrocution victims. Chest compressions don’t stimulate electrical signals and won’t be effective.

Many HVAC techs work alone, but if they’re working in teams, they should know how to use an AED.


How can you prevent electrocution?

Apart from avoiding live electrical systems altogether, there’s a strategy that electricians use to prevent currents from crossing their hearts: the “Left Hand Rule.”

The Left Hand Rule is pretty simple and only involves your left hand (if you are right-handed) and a pocket at the front of your pants. You keep your left hand in your pocket while touching an energized component with a meter or similar device. 

It’s quite a simple method, but it removes a path for current flow across the heart. The shock will travel from your right hand to the ground instead of across your body (and heart) to your left hand. It’s not foolproof, and you’ll still likely suffer an injury of some kind, but it cuts off a pathway for the current to travel across your chest to find an exit point.

At HVAC School, we don’t ever recommend working with live electricity when it’s avoidable. However, if there is ever a case when you must work on a live system, you can hopefully use some of this knowledge to be safe around live electricity. You may even save a teammate’s life (or your own).




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