How Do Chest Compressions Actually Work?

Are you really pumping the heart?

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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.

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 will explore how blood vessels transport blood throughout the body and how CPR chest compressions can be used save a life.

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

The 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 emergency medical services (EMS) arrives.

If someone collapses and is unresponsive when you yell "Are you OK?" and doesn't seem to be breathing, call 9-1-1 or direct another person to call. Then, follow the steps of CPR:

  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 recoil, or return to its original shape, after each press of your hands.
  3. Give rescue breaths. If you've received training and feel comfortable giving rescue breaths, then give two rescue breaths after 30 chest compressions to help get oxygen into their 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 an automated external defibrillator (AED) or EMS arrives.

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. 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.

An AED is a portable device that can be used by the public. You place its pads on the person's chest and the device analyzes the heart rhythm and delivers a shock to the heart if sensors indicate that it's needed.

If someone goes into cardiac arrest in a public space, ask if there is an AED nearby.

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

Part of the misunderstanding about the role of chest compressions comes from names to describe it, such as external cardiac massage and closed-chest cardiac massage.

Historically, these names signaled an alternative option to internal cardiac massage—basically the doctor cut open your chest, reached in, and squeezed—that was commonly used in the early 20th century.

Chest compressions mimic the heart's pumping, but how exactly they keep the blood flowing still isn't fully understood and is likely based on multiple factors.

One of those factors is that chest compressions can help squeeze blood into vessels.

To better understand how blood may flow during CPR, it helps to understand 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 the whole thing along.

Blood Vessels 101

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

  • Capillaries are the smallest blood vessels, and they’re so tiny that red blood cells have to go through them one at a time. It’s helpful to think of capillaries as the channels running through a sponge that soak up fluid. Capillaries form the connection between arteries and veins.
  • Arteries are the vessels that carry 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 the flow.
  • Veins collect blood from other tissues and ferry it back to the heart. These vessels deal with much lower pressures than arteries do and have thinner walls. To keep the blood moving with such little pressure, veins have valves that only allow blood to flow in one direction. These valves can help chest compressions to be effective.

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 arteries that carry blood to the heart muscle—can increase the risk of heart attacks and strokes.

A heart attack blocks blood flow to the heart and it is not the same thing as cardiac arrest. Although, a person having a heart attack can then go into sudden cardiac arrest.

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

Arteries
  • Carry blood away from heart

  • Deal with high pressures

  • Can expand and constrict 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

Understanding how blood vessels work will help you see how that may translate into blood flow during compressions.

Body tissues and muscles act like sponges. When you squeeze a soaked sponge, fluid oozes out of it. In the case of body tissues, squeezing forces blood out. Blood getting squeezed out of the tissues can go into the veins or arteries.

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

The heart is included in this one-way valve business. Each of the chambers of the heart has a valve. Once blood leaves a heart chamber, it's not allowed back in until it goes all the way around the body and back.

You might not be pumping the heart directly during compressions, but you may be able to squish the chambers closed.

Chest Compressions Have Two Parts

Squishing blood out of the tissues isn't the only way that blood is encouraged to flow when you're doing chest compressions.

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

Just like in a sponge, when you release the squished tissues, they suck up fluid. Plus, since the chambers of the heart are roughly in the middle of the chest and they have those nifty one-way valves in them, they may suck up blood as well during recoil.

There is a lot of evidence that the sucking action of recoil between chest compressions is just as important during CPR as pushing.

One of the theories of why hands-only CPR is so successful has to do with the fact that nobody is blowing into the chest and reducing its ability to suck blood in.

Besides, 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

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.

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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6 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.
  1. Centers for Disease Control and Prevention. Three things you may not know about CPR. Updated January 4, 2021.

  2. American Heart Association. History of CPR.

  3. American Red Cross. CPR steps.

  4. Cipani S, Bartolozzi C, Ballo P, Sarti A. Blood flow maintenance by cardiac massage during cardiopulmonary resuscitation: Classical theories, newer hypotheses, and clinical utility of mechanical devicesJournal of the Intensive Care Society. 2019;20(1):2-10. doi:10.1177/1751143718778486

  5. National Cancer Institute. Classifications & structure of blood vessels.

  6. Rajab TK, Pozner CN, Conrad C, Cohn LH, Schmitto JD. Technique for chest compressions in adult CPRWorld J Emerg Surg. 2011;6:41. Published 2011 Dec 10. doi:10.1186/1749-7922-6-41