How Do Chest Compressions Actually Work?

Are you really pumping the heart?

There's a common misunderstanding that the main point of cardiopulmonary resuscitation (CPR) chest compressions is to directly pump the heart to get it beating again.

However, the heart typically needs an electric shock in order to restart. It's also deep in the chest.

One person performing chest compressions on another outside on a sunny day
Science Photo Library / Getty Images

Instead, the main goal of chest compressions is to help restore blood flow to the brain and other vital organs, including the lungs and the heart itself, until the heart can be shocked.

This article explores how blood vessels transport blood throughout the body and how CPR chest compressions can be used to save a life.

CPR Steps and What They Do

If someone's heart suddenly stops, known as sudden cardiac arrest, they can die within minutes. Blood isn't getting to their brain and other vital organs.

When CPR is performed quickly, it can double or triple a person's chance of survival. It can also help prevent or reduce brain damage by keeping blood flowing to the brain in the minutes before the emergency medical services (EMS) team arrives.

CPR should be performed if someone collapses, is unresponsive when you ask if they are OK, and doesn't seem to be breathing. Before beginning, be sure to call 911 or direct another person to do so.

Here are the steps to follow:

  1. Place your hands on the center of their chest with one hand on top of the other. Center your weight over you hands.
  2. Perform chest compressions to help restore blood flow to vital organs. Use your body weight to firmly press at least 2 inches deep (but no deeper than 2.4 inches) at a rate of about 100 to 120 compressions per minute. Allow the chest to return to its original position after each press of your hands.
  3. Give rescue breaths. If you've received training and feel comfortable giving rescue breaths, give two rescue breaths after 30 chest compressions to help get oxygen into the body.
  4. Repeat the cycle of chest compressions and rescue breaths in cycles of 30 chest compressions and two breaths, or just do continuous chest compressions, until EMS arrives.

Using an AED

If you are in a public setting, ask someone to see if there is an automated external defibrillator (AED) nearby. This is a portable device that can be used by the public.

You place its pads on the person's chest. The device analyzes the heart rhythm and delivers a shock to the heart if sensors indicate that it's needed.

If one is at the ready, use it immediately, then begin CPR. Leave the pads in place and follow the instructions on the device.

If one is not right there for you to use, do not delay starting CPR. Every minute counts.

Hands-Only CPR

If you haven't taken a CPR training to learn how to do CPR, or if you're unsure about giving rescue breaths, then use hands-only CPR.

This involves compressing the chest as with traditional CPR, but not stopping to administer breaths.

Chest compressions are considered the most essential part of CPR since it can get blood to the brain to help prevent brain damage and death.

One of the theories as to why hands-only CPR is so successful is that taking time to blow into someone's mouth may interrupt gains in blood flow from the compressions.

For patients who collapse from sudden cardiac arrest, there's often plenty of oxygen left in the bloodstream so mouth to mouth isn't really necessary.

Recap

CPR can double or triple a person's chance of survival, especially if it's started immediately after someone goes into cardiac arrest. CPR chest compressions can help restore blood flow to the brain, heart, and other vital organs.

How CPR Chest Compressions Work

In the early 20th century, internal cardiac massage was a common technique used for cardiac arrest patients. This involved a doctor cutting open the chest, reaching in, and squeezing the heart with their hands.

While still done in select emergency situations in a hospital setting, this practice is less common today thanks to CPR (which was developed in 1960).

Part of the misunderstanding about the role of chest compressions comes from the fact that its alternative names—external cardiac massage and closed-chest cardiac massage—are so similar to internal cardiac massage.

Chest compressions mimic the heart's pumping, but how exactly they keep the blood flowing still isn't fully understood. It's likely based on several factors, including that chest compressions can help squeeze blood into vessels.

To better understand how blood may flow during CPR, it helps to get a sense of the general functioning of blood vessels.

All types of blood vessels help guide blood flow through the chest cavity during CPR, but veins in particular play an important role in moving things along.

Blood Vessels 101

The vessels that carry blood around your body are roughly categorized into one of three types:

  • Arteries are the vessels that carry oxygenated blood away from the heart. These are high-pressure "pipes" with thick walls that have the ability to expand or constrict in order to help control flow.
  • Veins collect blood that needs oxygen from other tissues and ferry it back to the heart. These vessels deal with much lower pressures than arteries and have thinner walls. To keep blood moving with such little pressure, veins have valves that only allow blood to flow in one direction. These can help chest compressions be effective.
  • Capillaries connect the arteries and veins. They deliver oxygen and nutrients in your blood to your organs and tissues and remove waste products, including carbon dioxide. They are the smallest blood vessels—so tiny, in fact, that red blood cells have to go through them one at a time.

As you age, crusts called plaques form on the inside of arteries. This happens a little in everyone, but a lot of plaque buildup—especially in the coronary arteries that wrap around the outside of the heart muscle and keep it pumping—can increase the risk of heart attacks and strokes.

A heart attack blocks blood flow to the heart and is not the same as cardiac arrest. That said, a person can go into sudden cardiac arrest after having a heart attack.

During a heart attack, a person is still breathing and talking. They don't need CPR, but they do need to get immediately to a hospital.

Arteries
  • Carry blood away from heart (coronary arteries carry blood from the heart to nourish the heart itself)

  • Deal with high pressures

  • Can expand and contract to control blood flow

Veins
  • Carry blood toward the heart

  • Deal with low pressures

  • Have valves that keep blood flowing in one direction

Blood Flow by Compression

Knowing how blood vessels work can help you better understand how blood flows during CPR compressions.

Body tissues and muscles act like sponges. Squeezing them forces liquid—in this case, blood—out. That blood then goes back into circulation.

Blood that goes into the veins can't go backward because of their valves. After a few compressions, though, there's likely enough pressure to start moving blood through the veins and even back to the heart itself.

The heart poses a similar issue. Each of its four chambers has a valve. Once blood leaves one chamber, it's on a one-way trip around the body and is only allowed back in after that journey is done.

You might not be pumping the heart directly during compressions, but you may be able to squish the chambers or generate enough pressure to eject some blood that wouldn't otherwise be moving.

Chest Compressions Have Two Parts

As important as it is to push on the chest to get blood moving, it's also important to allow the chest to recoil.

Getting back to our sponge analogy, when you stop squishing tissues, they suck up more blood. This means there may be more blood to squeeze into circulation on the next compression. And since the chambers of the heart are roughly in the middle of the chest, they may also suck up blood that can then be moved during the next compression.

There is a lot of evidence that what happens between chest compressions is just as important during CPR as the compressions themselves.

Recap

Veins have valves that only allow blood to flow in one direction, which can be helpful in distributing blood during chest compressions. The body tissues also act like sponges, squeezing out blood that can move into blood vessels.

Summary

CPR chest compressions can save a person's life by helping to restore blood flow to the brain and other vital organs until the heart can be restarted.

How chest compressions accomplish this isn't fully understood, but it's likely that blood is squeezed from tissues into vessels and pressure is generated that gets blood moving.

Chest compressions mimic the heart's pumping and can double or triple a person's chance of survival after cardiac arrest.

A Word From Verywell

You can perform CPR chest compressions regardless of training, but practicing how to respond can help you feel prepared and confident that you'll known what to do in an emergency situation.

Find a CPR training class in your area through the American Red Cross or American Heart Association.

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5 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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