Your Guide to How the Circulatory System Works

Medically Reviewed By Dr. Payal Kohli, M.D., FACC

Your heart is an organ about the size of your fist. It is the central pump of your circulatory system, pumping about 5 liters of blood per minute. Your circulatory system transports oxygen and nutrients all over your body. This article talks about how the circulatory system works, its parts, and the functions each part performs. It also discusses health conditions that can affect the circulatory system.

How does the circulatory system work?

This shows a picture of a heart.
CACTUS Creative Studio/Stocksy United

The circulatory system, also called the cardiovascular system, is a closed-loop system of blood vessels and your heart. The circulatory system is imperative for survival. It is one of the first systems developed in an embryo, starting the heart rate at only 4 weeks. 

The heart acts as a pump, beating an average of 60–100 times Trusted Source American Heart Association Highly respected national organization Go to source every minute. Each beat ejects oxygen-rich blood out into the arteries to travel to all the body’s cells. The blood travels through tiny capillaries and then into the veins, where it starts its journey back to the heart.

Once in the heart again, the blood travels through two heart chambers before traveling through the lungs, picking up more oxygen. After getting oxygen, it travels back into the heart before leaving for the rest of the body. 

What are the parts of the circulatory system?

The parts of the circulatory system include:

  • Heart: The heart is the central part of the circulatory system. Without the heart pumping, the system would not work properly.
  • Blood vessels: The blood vessels hold the blood and make a closed-loop going to and from the heart. 
  • Blood: The blood carries oxygen, nutrients, hormones, and waste products around the body.

What does the circulatory system do?

The circulatory system makes sure that every cell in the body has the oxygen and nutrients it needs to survive. It also removes the waste products from the cells. 

What are the parts of the heart?

Three muscle layers make up the heart. Inside are four chambers, two atria on top and two ventricles on the bottom. The septum wall is in the heart’s center, separating the chambers. 

Blood comes from the body through the vena cava and into the right atrium. Next, it travels through a valve and into the right ventricle before exiting and going to the lungs.

In the lungs, the blood is reoxygenated and then enters back into the heart via the left atrium. Lastly, it travels through the left ventricle before being pumped out into the body. 

What does the heart do?

The heart is a muscular pump, providing the force to circulate the blood all around the body. Without the heart beating, the cells of the body can die quickly. 

The heart has an internal electrical system that manages the rate and rhythm of the heart. The cardiac center in the brain can also influence the pace and rhythm.

The contraction of the atria and ventricles leads to each heartbeat. If you use a stethoscope to listen to your heart, it sounds like “lub-DUB.” The “lub” sound comes from the valves near the atria closing when the blood flows into the ventricles. The “DUB” sounds come from the valves near the ventricles closing when the blood flows into the lungs or body.  

Looking after your heart

As your heart is a vital part of your body, it is important to care for it and keep it in good health.

Our Heart Health hub provides many articles and a lot of information about how to care for your heart, including:

What are the types of blood vessels?

There are three types of blood vessels: arteries, capillaries, and veins. 

  • Arteries are responsible for carrying oxygenated blood from the heart to the tissues of the body.
  • Capillaries are very tiny vessels with thin walls that allow oxygen to transfer to the cells.
  • Veins then carry the non-oxygenated blood back to the heart.

What conditions affect the circulatory system?

“Cardiovascular disease” is an umbrella term for several health conditions that affect the circulatory system Trusted Source American Heart Association Highly respected national organization Go to source .


Atherosclerosis involves plaque buildup on the walls of your arteries, making blood flow difficult. Sometimes it even blocks blood flow completely when a blood clot forms. This can cause a stroke or heart attack.

Learn more about atherosclerosis.

Heart attack

A heart attack happens when a blood clot blocks the blood flow to the heart muscle. Many people Trusted Source American Heart Association Highly respected national organization Go to source might survive their first heart attack, but your doctor can recommend a balanced diet, regular exercise, and self-care to help you to prevent a second one. 

Visit our Heart Attack hub for more information.

Heart failure

Heart failure, also called congestive heart failure, occurs when your heart does not beat as well as it should. If untreated, it can cause other health conditions and worsen. 

Find out more in our Heart Failure hub.


An arrhythmia is an irregular heart rhythm. There are several arrhythmias, and some are more dangerous than others. 

Bradycardia arrhythmias occur when your heart beats too slowly, and tachycardia arrhythmias happen when your heart beats too fast. 

Learn more about symptoms and causes of arrhythmia.

Heart valve problems

The valves of the heart sometimes do not open and close properly. This makes it harder for the blood to flow correctly through the heart. Learn more.

What are the symptoms of circulatory problems?

When your circulatory system works incorrectly, your body’s cells do not receive enough oxygen, which leads to cardiovascular health concerns. Some common symptoms of these concerns include:

  • chest pain, tightness, or heaviness
  • shortness of breath
  • pain in your neck, shoulders, or arms
  • nausea
  • sweats
  • dizziness or lightheadedness
  • lower leg swelling
  • sensation of heart racing
  • anxiety

How are circulatory system conditions diagnosed?

If you experience any symptoms of problems with your cardiovascular system, you will need to contact your healthcare professional.

The initial physical exam will let you know if your blood pressure and heart rate are stable and if your heart rhythm is correct. Then, after reviewing your medical history and medications, several tests can help determine what is going on. 

Blood work

Your labs can give information about what is going on, such as your cholesterol level. In addition, your troponin level tells you if a heart attack damaged your heart muscle, and a BNP or pro-BNP tells you about stretch or higher pressures in the chambers of the heart.

Labs can also check how well your blood clots and if your electrolytes are balanced.


For this test, medical professionals attach small sensors to your skin to track the electrical activity of your heart. The electrocardiogram (ECG) can track how the heart beats and provides information about arrhythmias, heart attacks, heart disease, and heart failure. 

Find out more.


An X-ray is usually a quick and painless way to get a picture of what is going on inside your body. A chest X-ray can show Trusted Source American Heart Association Highly respected national organization Go to source an enlargement of your heart or chest congestion. 


Also called an “echo,” this test is an ultrasound of the heart. It can show how well the heart muscle beats and if enough blood ejects out, called the ejection fraction. 

Learn more.

MRI scan

For an MRI test, you will lie down on a table that slides into a tube-like machine that takes detailed pictures of the inside of your body. The machine can be very loud, so medical professionals will give you earplugs.

A microphone allows you to stay in contact with the technician. The images of the MRI show the structures of your heart and if there is any damage. 

CT scan

CT scans, sometimes called “cat scans,” use X-ray to take detailed pictures of your body, including your heart and blood vessels. 

Exercise stress test

For an exercise stress test, medical professionals attach you to some equipment to monitor your heart while you walk on a treadmill. At first, the technician starts you on a slow rate, then speeds the rate up. The technician also usually uses an incline as part of the protocol.

This test shows how your heart performs under stress. 

Radionuclide ventriculography 

For this test, a doctor injects a radioactive tracer into your bloodstream. This allows them to see how much blood your heart muscle gets and also how much blood the heart pumps.

Cardiac catheterization

A doctor will insert a catheter, which is a very small tube, into a blood vessel in your arm or thigh and then position it near the top of your heart.

Once in place, they will inject a dye into your heart so they can see blockages or narrowed arteries in your heart. 

When should I contact a doctor for circulatory system symptoms?

Be sure to let your healthcare professional know if you notice symptoms of cardiovascular problems, such as:

  • chest pain, tightness, or heaviness
  • shortness of breath
  • pain in your neck, shoulders, or arms
  • nausea
  • sweats
  • dizziness or lightheadedness
  • lower leg swelling
  • sensation of racing heart
  • anxiety
  • nighttime awakening due to shortness of breath
  • difficulty breathing comfortably at night without extra pillows

Serious symptoms of cardiovascular problems include:

  • chest pain lasting more than a few minutes, or returning after going away
  • chest pressure or squeezing
  • pain in your neck, jaw, arms, or stomach
  • shortness of breath with or without chest pain
  • other possible symptoms: cold sweat, nausea, feeling light-headed

Get immediate medical help if you experience severe cardiovascular symptoms.


Your cardiovascular system is an essential part of your body. Each cell benefits from your heart pumping your blood and bringing oxygen and nutrients to them.

Several medical conditions can affect your circulatory system. It is beneficial to take steps to keep your cardiovascular system healthy. 

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Medical Reviewer: Dr. Payal Kohli, M.D., FACC
Last Review Date: 2022 May 26
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