How do chest compressions actually work?

There is a common misconception that the main purpose of chest compressions in cardiopulmonary resuscitation (CPR) is to directly pump the heart to make it beat again.

However, the heart usually needs a shock 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 receives an electric shock.

This article discusses how blood vessels carry blood throughout the body and how CPR chest compressions can be used to save lives.

CPR steps and their effects

If someone’s heart stops suddenly, called cardiac arrest, they can die within minutes. Blood cannot get to their brains and other vital organs.

If CPR is performed quickly, it can double or triple a person’s chances of survival. It can also help prevent or reduce brain damage by maintaining blood flow to the brain in the minutes before emergency medical services (EMS) teams arrive.

If someone falls, doesn’t respond when you ask if they’re okay, and doesn’t seem to be breathing, give CPR. Be sure to call 911 or instruct others to do so before you begin.

Here are the steps to follow:

  1. Place your hand on the center of their chest, one hand on top of the other. Concentrate your weight on your hands.
  2. Perform chest compressions to help restore blood flow to vital organs. Use your body weight to press at least 2 inches deep (but no more than 2.4 inches) at a rate of about 100 to 120 compressions per minute. After each hand press, allow the chest to return to its original position.
  3. Take rescue breaths. If you are trained and feel comfortable giving rescue breaths, give two rescue breaths after 30 chest compressions to help draw oxygen into your body.
  4. Repeat the cycle of chest compressions and rescue breaths in a cycle of 30 chest compressions and two breaths, or just continuous chest compressions until EMS arrives.

Using an AED

If you are in a public place, ask someone to see if there is an automated external defibrillator (AED) nearby. This is a portable device available for public use.

You put its pad on the person’s chest. The device analyzes the heart rhythm and delivers shocks to the heart when sensors indicate the need.

If you are ready, use it immediately and start CPR. Leave the pad in place and follow the instructions on the device.

If one is not suitable for you, do not delay starting CPR. Every minute counts.

Manual CPR

If you have no CPR training to learn how to perform CPR, or if you are unsure whether to give artificial respiration, use manual-only CPR.

This includes compressing the chest like traditional CPR, but without stopping to breathe.

Chest compressions are considered the most important part of CPR because it delivers blood to the brain to help prevent brain damage and death.

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

For patients who pass out from cardiac arrest, there is usually a lot of oxygen left in the blood, so mouth-to-mouth isn’t really needed.


CPR can double or triple a person’s chances of survival, especially if it is started immediately after someone has had a cardiac arrest. CPR chest compressions can help restore blood flow to the brain, heart, and other vital organs.

Can you compress your chest too quickly during CPR?

How CPR chest compressions work

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

Although still performed in specific emergency situations in hospital settings, the practice is less common today due to CPR (developed in 1960).

Part of the misconception about the action of chest compressions comes from its alternate names—external heart massage and closed-chest heart massage—which are very similar to internal heart massage.

Chest compressions simulate the beating of the heart, but exactly how they keep blood flowing is still not fully understood. This may be based on several factors, including that chest compressions can help squeeze blood into the blood vessels.

To better understand how blood flows during CPR, it is helpful to understand the general function 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 objects.

Vascular 101

The blood vessels that carry blood around your body are broadly classified into one of three types:

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

As we age, scabs called plaques form inside the arteries. This happens to everyone a little bit, but large buildup of plaque — especially in the coronary arteries that surround the outside of the heart muscle and keep pumping — can increase the risk of heart attack and stroke.

A heart attack stops blood flow to the heart, unlike a cardiac arrest. That is, a person may experience sudden cardiac arrest after a heart attack.

During a heart attack, a person is still breathing and talking. They don’t need CPR, but they do need to go to the hospital right away.


  • Takes blood from the heart (coronaries take blood from the heart to nourish the heart itself)

  • coping with high pressure

  • Can expand and contract to control blood flow


  • deliver blood to the heart

  • coping with low pressure

  • have valves that keep blood flowing in one direction

compressed blood flow

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

Body tissues and muscles are like sponges. Squeezing them forces fluid — in this case blood — out. The blood then re-enters the circulation.

Blood entering the vein cannot flow back due to its valves. However, after a few compressions, there may be enough pressure to start pushing blood through the veins and even back to the heart itself.

Heart asks similar questions. Each of its four chambers has a valve. Once blood leaves a room, it makes a one-way trip around the body and can only return when the trip is complete.

You may not pump the heart directly during compressions, but you may be able to squeeze the chambers or create enough pressure to expel some blood that wouldn’t otherwise move.

There are two parts to chest compressions

It’s important to push your chest to get the blood flowing, and it’s also important to let your chest sit back.

Going back to our sponge analogy, when you stop squeezing tissues, they absorb more blood. This means that more blood may enter the circulation at the next compression. And because the heart’s chambers are roughly in the middle of the chest, they may also absorb blood, which can then be moved with the next compression.

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


Veins have valves that allow blood to flow in only one direction, which helps distribute blood during chest compressions. Body tissue also acts like a sponge, squeezing out blood that can enter blood vessels.


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

How chest compressions accomplish this is not fully understood, but it is likely that blood is squeezed from the tissue into the blood vessels and creates pressure that keeps the blood flowing.

Chest compressions, which simulate the beating of the heart, can double or triple a person’s chances of survival after cardiac arrest.

VigorTip words

You can perform CPR chest compressions regardless of training, but practicing how to respond can help you prepare and feel confident knowing what to do in an emergency.

Find CPR classes in your area through the American Red Cross or American Heart Association.