The human heart pumps blood to every part of your body. Learn about the different parts of the heart and watch our video about how a healthy heart works.
Your heart is the pump which powers your body. It supplies blood carrying oxygen and nutrients to every cell, nerve, muscle and vital organ in your body.
It sits in your chest between your lungs, slightly to the left of centre, and is protected by your rib cage.
Your heart is about the size of your clenched fist and weighs about 300 grams (that's just over half a packet of butter).
Watch our step-by-step video of how the heart works
What are the parts of the heart?
Your heart is a bit like a house. It has:
Heart walls
The walls of your heart are made of powerful muscle tissue, which squeezes and relaxes to pump blood around your body. This muscle tissue is divided into three layers.
- The endocardium (the inside layer).
- The myocardium (the muscular middle layer).
- The epicardium (the protective outer layer).
Heart chambers (rooms)
Your heart is made up of four chambers, two on the right and two on the left. These are like the rooms of your house.
The top two chambers are called the left and right atrium and the bottom two are called the left and right ventricles.
They are divided by a thin wall called the septum.
Heart valves (the doors between the rooms)
There are four heart valves, which act like doors between the chambers of the heart. They open and close as your heart pumps.
The valves only open one way. This stops blood flowing in the wrong direction between the chambers of your heart.
The two valves that sit between the upper and lower chambers of the heart are called the atrioventricular, or AV valves.
The tricuspid valve is the door between the right atrium and ventricle.
The mitral valve is the door between the left atrium and ventricle.
The other two valves are the doors out of the ventricles. They are called semilunar, or SL valves.
The aortic valve is the door out of the left ventricle into the aorta.
The pulmonary valve is the door out of the right ventrical into the pulmonary artery.
The blood vessels (the plumbing)
Blood travels between the heart and the lungs and the rest of the body, via a network of pipes called the blood vessels. There are three main types of blood vessels.
- Arteries, which carry oxygenated blood from your heart to the rest of your body.
- Veins, which carry the de-oxygenated blood back to your heart and lungs.
- Capillaries, the small vessels where oxygenated and de-oxygenated blood is exchanged.
How the heart pumps
Your conduction system sends the electrical signals which trigger the heart to pump blood around the body, and to and from the lungs.
Blood which has used all its oxygen is returned to the right side of the heart, via large veins called the inferior and superior vena cava. From there it is pumped to the lungs, via the pulmonary artery.
Once the blood has received oxygen from the lungs, it travels through the pulmonary veins into the left side of the heart. From here it is pumped back out around the body, via the aorta.
The heart's conduction system (the electrics)
Your heart has its own electrical wiring system (conduction system), which keeps it beating. This conduction system includes:
- the sinoatrial (SA) node (or sinus node). This is your body’s own internal pacemaker, that produces electrical signals to make your heart beat
- the atrioventricular (AV) node. This is a node that passes on the electrical signals from the upper chambers of the heart (artia) to the lower ones (ventricles)
- the bundle of His, the left and right bundle branches, and the Purkinje fibres. These act like electrical wiring that communicate the signals around the heart.
The SA node sends an electrical signal that makes the upper chambers of the heart (atria) contract (squeeze). This pushes blood out of the atria and into the lower chambers of the heart (ventricles).
The electrical signal passes from the atria to the AV node. From there, it passes through the bundle of His and into the right and left bundle branches.
Finally, the signal travels down the Purkinje fibres, causing the ventricles to contract. This pushes blood out of your heart to your lungs and the rest of your body.
How the heart pumps
Your conduction system sends the electrical signals which trigger the heart to pump blood around the body, and to and from the lungs.
Blood which has used all its oxygen is returned to the right side of the heart, via large veins called the inferior and superior vena cava. From there it is pumped to the lungs, via the pulmonary artery.
Once the blood has received oxygen from the lungs, it travels through the pulmonary veins into the left side of the heart. From here it is pumped back out around the body, via the aorta.
The coronary arteries
The heart has its own network of blood vessels, which supply it with the blood it needs to keep pumping.
These vessels are called the coronary arteries. They branch off the body’s largest artery, the aorta, and lie on the outside of your heart.
Narrowing in one of the coronary arteries can lead to angina and a blockage can cause a heart attack.
Learn about heart conditions
What is your pulse?
The pulse you can feel, for example in your wrist or neck, is the heart pumping blood. You can measure the rate and rhythm of your heart by taking your pulse.
How to take your pulse
The circulatory system (cardiovascular system) pumps blood from the heart to the lungs to get oxygen. The heart then sends oxygenated blood through arteries to the rest of the body. The veins carry oxygen-poor blood back to the heart to start the circulation process over. Your circulatory system is critical to healthy organs, muscles and tissues.
Your heart and blood vessels make up the circulatory system. The main function of the circulatory system is to provide oxygen, nutrients and hormones to muscles, tissues and organs throughout your body. Another part of the circulatory system is to remove waste from cells and organs so your body can dispose of it.
Your heart pumps blood to the body through a network of arteries and veins (blood vessels). Your circulatory system can also be defined as your cardiovascular system. Cardio means heart, and vascular refers to blood vessels.
The circulatory system provides blood to all the body's tissues so they can function.
The circulatory system’s function is to move blood throughout the body. This blood circulation keeps organs, muscles and tissues healthy and working to keep you alive.
The circulatory system also helps your body get rid of waste products. This waste includes:
- Carbon dioxide from respiration (breathing).
- Other chemical byproducts from your organs.
- Waste from things you eat and drink.
How does the circulatory system work?
Your circulatory system functions with the help of blood vessels that include arteries, veins and capillaries. These blood vessels work with your heart and lungs to continuously circulate blood through your body. Here’s how:
- The heart’s bottom right pumping chamber (right ventricle) sends blood that’s low in oxygen (oxygen-poor blood) to the lungs. Blood travels through the pulmonary trunk (the main pulmonary artery).
- Blood cells pick up oxygen in the lungs.
- Pulmonary veins carry the oxygenated blood from the lungs to the heart’s left atrium (upper heart chamber).
- The left atrium sends the oxygenated blood into the left ventricle (lower chamber). This muscular part of the heart pumps blood out to the body through the arteries.
- As it moves through your body and organs, blood collects and drops off nutrients, hormones and waste products.
- The veins carry deoxygenated blood and carbon dioxide back to the heart, which sends the blood to the lungs.
- Your lungs get rid of the carbon dioxide when you exhale.
The parts of your circulatory system are your:
- Heart, a muscular organ that pumps blood throughout your body.
- Blood vessels, which include your arteries, veins and capillaries.
- Blood, made up of red and white blood cells, plasma and platelets.
What are the circulatory system circuits?
Your circulatory system has three circuits. Blood circulates through your heart and through these circuits in a continuous pattern:
- The pulmonary circuit: This circuit carries blood without oxygen from the heart to the lungs. The pulmonary veins return oxygenated blood to the heart.
- The systemic circuit: In this circuit, blood with oxygen, nutrients and hormones travels from the heart to the rest of the body. In the veins, the blood picks up waste products as the body uses up the oxygen, nutrients and hormones.
- The coronary circuit: Coronary refers to your heart’s arteries. This circuit provides the heart muscle with oxygenated blood. The coronary circuit then returns oxygen-poor blood to the heart’s right upper chamber (atrium) to send to the lungs for oxygen.
What are the types of blood vessels?
There are three main types of blood vessels:
- Arteries: Arteries are thin, muscular tubes that carry oxygenated blood away from the heart and to every part of your body. The aorta is the body’s largest artery. It starts at the heart and travels up the chest (ascending aorta) and then down into the stomach (descending aorta). The coronary arteries branch off the aorta, which then branch into smaller arteries (arterioles) as they get farther from your heart.
- Veins: These blood vessels return oxygen-depleted blood to the heart. Veins start small (venules) and get larger as they approach your heart. Two central veins deliver blood to your heart. The superior vena cava carries blood from the upper body (head and arms) to the heart. The inferior vena cava brings blood up from the lower body (stomach, pelvis and legs) to the heart. Veins in the legs have valves to keep blood from flowing backward.
- Capillaries: These blood vessels connect very small arteries (arterioles) and veins (venules). Capillaries have thin walls that allow oxygen, carbon dioxide, nutrients and waste products to pass into and out of cells.
What are the circulatory system organs?
Your heart is the only circulatory system organ. Blood goes from the heart to the lungs to get oxygen. The lungs are part of the respiratory system. Your heart then pumps oxygenated blood through arteries to the rest of the body.
Many conditions can affect the health of your circulatory system, including:
- Aneurysms: Aneurysms occur when an artery wall weakens and enlarges. The weak spot can bulge as blood moves through the artery. The weak spot may tear, causing a life-threatening rupture. Aneurysms can affect any artery, but aortic aneurysms, abdominal aortic aneurysms and brain aneurysms are the most common.
- High blood pressure: Your arteries work hard to circulate blood throughout the body. When the pressure (force of blood against the blood vessel walls) gets too high, you develop high blood pressure. When the arteries become less elastic (stretchy), less blood and oxygen reaches organs like the heart. High blood pressure puts you at risk for cardiovascular disease, heart attacks and strokes.
- Plaque deposits: High cholesterol and diabetes can lead to fat and other substances collecting in the blood. These substances form deposits called plaques on artery walls. This condition is atherosclerosis, or narrowed or hardened arteries. Atherosclerosis increases the risk of blood clots and strokes, coronary artery disease, peripheral artery disease (and other artery diseases), heart attacks and kidney disease.
- Venous disease: Venous diseases tend to affect veins in the lower body. Problems like chronic venous insufficiency and varicose veins occur when blood can’t flow back to the heart and pools in leg veins. Deep vein thrombosis (DVT), a blood clot in the legs, can lead to a life-threatening pulmonary embolism.
These steps can protect the health of your circulatory system:
- Aim for at least 150 minutes of physical activity every week.
- Eat a heart-healthy diet rich in vegetables and fiber and low in saturated fats and processed foods. Consider a Mediterranean-style diets or plant-based diet, as they appear to be the most heart healthy.
- Find healthy ways to ease stress.
- Maintain a healthy weight.
- Manage conditions like diabetes, high blood pressure and high cholesterol.
- Get help to quit smoking.
Your body has more than 60,000 miles of blood vessels that circulate about 1.5 gallons of blood every day.
What is red blood and blue blood?
All blood is red. Hemoglobin, an iron-rich protein in red blood cells, mixes with oxygen to give blood its red color. Blood that’s rich in oxygen is known as red blood.
Your veins carry oxygen-poor blood. This is sometimes called blue blood because your veins can look blue underneath the skin. The blood is actually red, but the low oxygen levels give veins a bluish hue.
Do arteries always carry oxygenated blood?
For the most part, yes. The exceptions are pulmonary arteries and veins. Pulmonary arteries carry deoxygenated blood to the lungs. Pulmonary veins return the oxygenated blood to the heart.
A note from Cleveland Clinic
Your circulatory system plays a critical role in keeping you alive. Blood vessels carry blood to the lungs for oxygen. Then your heart pumps oxygen-rich blood through arteries to the rest of the body. Your veins help your body get rid of waste products. Conditions like high blood pressure, high cholesterol and atherosclerosis can affect the health of your circulatory system. If you have one of these conditions, talk to your healthcare provider about steps you can take to protect your cardiovascular health.
Last reviewed by a Cleveland Clinic medical professional on 09/21/2021.
References
- InformedHealth.org. How does the blood circulatory system work? (//www.ncbi.nlm.nih.gov/books/NBK279250/) Accessed 10/6/2021.
- Merck Manual (Consumer Version). Biology of the Blood Vessels. (//www.merckmanuals.com/home/heart-and-blood-vessel-disorders/biology-of-the-heart-and-blood-vessels/biology-of-the-blood-vessels) Accessed 10/6/2021.
- Merck Manual (Consumer Version). Biology of the Heart. (//www.merckmanuals.com/home/heart-and-blood-vessel-disorders/biology-of-the-heart-and-blood-vessels/biology-of-the-heart) Accessed 10/6/2021.
- National Cancer Institute. Circulatory Pathways. (//training.seer.cancer.gov/anatomy/cardiovascular/blood/pathways.html) Accessed 10/6/2021.
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