How the heart works | NHS inform

Your heart is roughly the size of a fist and sits in the middle of your chest, slightly to the left.

It’s the muscle at the centre of your circulation system. It pumps blood around your body as your heart beats. This blood sends oxygen and nutrients to all parts of your body, and carries away unwanted carbon dioxide and waste products.

Structure of your heart

Your heart is made up of 3 layers of tissue:

• epicardium
• myocardium
• endocardium

These layers are surrounded by the pericardium, a thin outer lining protecting your heart.

There are 4 chambers that make up the heart – 2 on the left side and 2 on the right.

The 2 small upper chambers are the atria. The 2 larger lower chambers are the ventricles. These left and right sides of the heart are separated by a wall of muscle called the septum.

Circulatory system

Your heart pumps blood around the body all the time – about 5 litres (8 pints) of it. This is called circulation.

Your heart, blood and blood vessels together make up your cardiovascular system (or heart and circulatory system).

The right side of the heart receives blood that is low in oxygen because most has been used up by the brain and body. It pumps this to your lungs, where it picks up a fresh supply of oxygen. The blood then returns to the left side of the heart, ready to be pumped back out to the brain and the rest of your body.

Blood vessels

Your blood is pumped around your body through a network of blood vessels:

• arteries – they carry oxygen-rich blood from your heart to all parts of your body, getting smaller as they get further away from the heart
• capillaries – they connect the smallest arteries to the smallest veins, and help exchange water, oxygen, carbon dioxide and other nutrients and waste substances between the blood and the tissues around them
• veins – they carry blood, lacking in oxygen, back towards your heart, and get bigger as they get nearer your heart

Blood vessels are able to widen or narrow depending on how much blood each part of your body requires. This action is partly controlled by hormones.

Valves

Your heart has 4 valves:

• aortic valve – on the left side
• mitral valve – on the left side
• pulmonary valve – on the right side
• tricuspid valve – on the right side

These act like gates, keeping the blood moving in the right direction.

Electrical system 

For your heart to keep pumping regularly, it needs electrical signals which are sent to the heart muscle telling it when to contract and relax.

The electrical signal starts in the right atrium where your heart’s natural pacemaker (the sino–atrial node) is. This signal crosses the atria, making them contract. Blood is pumped through the valves into the ventricles.

Where the atria meet the ventricles, there is an area of special cells (called the atrio-ventricular node) which pass the electrical signals throughout your heart muscle by a system of electrical pathways, known as the conducting system.

The muscles of the ventricles then contract, and blood is pumped through the pulmonary and aortic valves into the main arteries.

The heart’s natural ‘pacemaker’ (the sino-atrial node) produces another electrical signal, and the cycle starts again.

Blood pressure

Blood pressure is the measurement of the pressure within the arteries. It plays a vital role in the way your heart delivers fresh blood to all your blood vessels. For blood to travel throughout your body quickly enough, it has to be under pressure. This is created by the relationship between 3 things:

• your heart’s pumping action
• the size and stretchiness of your blood vessels
• the thickness of the blood itself

One heartbeat is a single cycle in which your heart contracts and relaxes to pump blood. At rest, the normal heart beats approximately 60 to 100 times every minute, and it increases when you exercise.

To ensure an adequate blood supply around your body, the 4 chambers of your heart have to pump regularly and in the right sequence.

There are 2 phases to your heart’s pumping cycle:

• systole – this is when your heart contracts, pushing blood out of the chambers
• diastole – this is the period between contractions when the muscle of your heart (myocardium) relaxes and the chambers fill with blood

Further information on how the heart works

What can go wrong with heart function?

Structure

Some people are born with a heart that has not developed properly in the womb before birth. This is called congenital heart disease.

Sometimes you can inherit a heart condition from your family.

Cardiovascular system

Problems with your heart and circulation system include:

• heart attack
• angina
• stroke

Heart disease can happen when your coronary arteries become narrowed by a gradual build-up of fatty material – called atheroma.

If your coronary arteries are narrowed or blocked, the blood supply to your heart will be impaired. This is the most common form of heart disease, known as coronary heart disease (sometimes called coronary artery disease or ischaemic heart disease).

Eventually, your arteries may become so narrow they can’t deliver enough blood to your heart. This can cause angina – a pain or discomfort in your chest, arm, neck, stomach or jaw.

If the fatty material breaks off or ruptures, a blood clot will form. This can cause heart attack (or stroke, if the artery affected is carrying blood to your brain).

Electrical system

Normally your heart will beat between 60 to 100 times per minute. This regular rhythmic beating is dependent upon electrical signals being conducted throughout your heart.

If the electrical signals within your heart are interrupted, your heart can beat:

• too quickly (tachycardia)
• too slowly (bradycardia)
• in an irregular way

This is called arrhythmia. 

Further information on arrhythmia

Conditions affecting the pumping of your heart

There are some conditions that can damage your heart muscle. This makes it weak and unable to pump as efficiently as before. These conditions include:

• heart attack 
• high blood pressure (hypertension)
• heart valve problems
• cardiomyopathy – this is a general term for diseases of the heart muscle. Sometimes these diseases are inherited from your family. Sometimes they are caused by other things, like viral infections.

There are also conditions like high blood pressure (hypertension). This means your heart has to work harder.

When your heart muscle can’t meet your body’s demands for blood and oxygen, you can develop various symptoms, like:

• breathlessness
• extreme tiredness
• ankle swelling

This is called heart failure because of the failure of your heart to pump blood around the body and work efficiently.

Valves

Your heart can’t function normally if the heart valves aren’t working properly, as it can affect the flow of blood through the heart.

There are 2 main ways that the valves can be affected:

• valves can leak – this is called valve regurgitation or valve incompetence
• valves can narrow and stiffen – this is called valve stenosis

Anatomy and Circulation of the Heart

Written by WebMD Editorial Contributors

Medically Reviewed by Poonam Sachdev on April 24, 2023

• How Does the Heart Work?
• Where Is Your Heart?
• How Does Blood Flow Through the Heart?
• How Does Blood Flow Through Your Lungs?
• What Are the Coronary Arteries?
• How Does the Heart Beat?
• More

Your heart is an amazing organ. It continuously pumps oxygen and nutrient-rich blood throughout your body to sustain life. This fist-sized powerhouse beats (expands and contracts) 100,000 times per day, pumping 5 or 6 quarts of blood each minute, or about 2,000 gallons per day.

As the heart beats, it pumps blood through a system of blood vessels, called the circulatory system. The vessels are elastic tubes that carry blood to every part of the body.

Blood is essential. In addition to carrying fresh oxygen from the lungs and nutrients to your body’s tissues, it also takes the body’s waste products, including carbon dioxide, away from the tissues. This is necessary to sustain life and promote the health of all the body’s tissues.

There are three main types of blood vessels:

• Arteries. They begin with the aorta, the large artery leaving the heart. Arteries carry oxygen-rich blood away from the heart to all of the body’s tissues. They branch several times, becoming smaller and smaller as they carry blood farther from the heart.
• Capillaries. These are small, thin blood vessels that connect the arteries and the veins. Their thin walls allow oxygen, nutrients, carbon dioxide, and other waste products to pass to and from our organ’s cells.
• Veins. These are blood vessels that take blood back to the heart; this blood lacks oxygen (oxygen-poor) and is rich in waste products that are to be excreted or removed from the body. Veins become larger and larger as they get closer to the heart. The superior vena cava is the large vein that brings blood from the head and arms to the heart, and the inferior vena cava brings blood from the abdomen and legs into the heart.

Blood flows continuously through your body’s blood vessels. Your heart is the pump that makes it all possible.

The heart is under the rib cage, to the left of your breastbone (sternum) and between your lungs.

Looking at the outside of the heart, you can see that the heart is made of muscle. The strong muscular walls contract (squeeze), pumping blood to the arteries. The major blood vessels connected to your heart are the aorta, the superior vena cava, the inferior vena cava, the pulmonary artery (which takes oxygen-poor blood from the heart to the lungs where it is oxygenated), the pulmonary veins (which bring oxygen-rich blood from the lungs to the heart), and the coronary arteries (which supply blood to the heart muscle).

On the inside, the heart is a four-chambered, hollow organ. It is divided into the left and right side by a wall called the septum. The right and left sides of the heart are further divided into two top chambers called the atria, which receive blood from the veins, and two bottom chambers called ventricles, which pump blood into the arteries.

The atria and ventricles work together, contracting and relaxing to pump blood out of the heart. As blood leaves each chamber of the heart, it passes through a valve. There are four heart valves within the heart:

• Mitral valve
• Tricuspid valve
• Aortic valve
• Pulmonic valve (also called pulmonary valve)

The tricuspid and mitral valves lie between the atria and ventricles. The aortic and pulmonic valves lie between the ventricles and the major blood vessels leaving the heart.

The heart valves work the same way as one-way valves in the plumbing of your home. They prevent blood from flowing in the wrong direction.

Each valve has a set of flaps, called leaflets or cusps. The mitral valve has two leaflets; the others have three. The leaflets are attached to and supported by a ring of tough, fibrous tissue called the annulus. The annulus helps to maintain the proper shape of the valve.

The leaflets of the mitral and tricuspid valves are also supported by tough, fibrous strings called chordae tendineae. These are similar to the strings supporting a parachute. They extend from the valve leaflets to small muscles, called papillary muscles, which are part of the inside walls of the ventricles.

The right and left sides of the heart work together. The pattern described below is repeated over and over, causing blood to flow continuously to the heart, lungs, and body.

Right side of the heart

• Blood enters the heart through two large veins, the inferior and superior vena cava, emptying oxygen-poor blood from the body into the right atrium.
• As the atrium contracts, blood flows from your right atrium into your right ventricle through the open tricuspid valve.
• When the ventricle is full, the tricuspid valve shuts. This prevents blood from flowing backward into the atria while the ventricle contracts.
• As the ventricle contracts, blood leaves the heart through the pulmonic valve, into the pulmonary artery, and to the lungs where it is oxygenated.

Left side of the heart

• The pulmonary vein empties oxygen-rich blood from the lungs into the left atrium.
• As the atrium contracts, blood flows from your left atrium into your left ventricle through the open mitral valve.
• When the ventricle is full, the mitral valve shuts. This prevents blood from flowing backward into the atrium while the ventricle contracts.
• As the ventricle contracts, blood leaves the heart through the aortic valve, into the aorta, and to the body.

Once blood travels through the pulmonic valve, it enters your lungs. This is called the pulmonary circulation. From your pulmonic valve, blood travels to the pulmonary artery to tiny capillary vessels in the lungs.

Here, oxygen travels from the tiny air sacs in the lungs, through the walls of the capillaries, into the blood. At the same time, carbon dioxide, a waste product of metabolism, passes from the blood into the air sacs. Carbon dioxide leaves the body when you exhale. Once the blood is purified and oxygenated, it travels back to the left atrium through the pulmonary veins.

Like all organs, your heart is made of tissue that requires a supply of oxygen and nutrients. Although its chambers are full of blood, the heart receives no nourishment from this blood. The heart receives its own supply of blood from a network of arteries, called the coronary arteries.

Two major coronary arteries branch off from the aorta near the point where the aorta and the left ventricle meet:

• The right coronary artery supplies the right atrium and right ventricle with blood. It usually branches into the posterior descending artery, which supplies the bottom portion of the left ventricle and back of the septum with blood.
• The left main coronary artery branches into the circumflex artery and the left anterior descending artery. The circumflex artery supplies blood to the left atrium, side, and back of the left ventricle, and the left anterior descending artery supplies the front and bottom of the left ventricle and the front of the septum with blood.

These arteries and their branches supply all parts of the heart muscle with blood.

When the coronary arteries narrow to the point that blood flow to the heart muscle is limited (coronary artery disease), a network of tiny blood vessels in the heart that aren’t usually open called collateral vessels may enlarge and become active. This allows blood to flow around the blocked artery to the heart muscle, protecting the heart tissue from injury.

The atria and ventricles work together, alternately contracting and relaxing to make the heart beat and pump blood. The electrical system of your heart is the power source that makes this possible.

Your heartbeat is triggered by electrical impulses that travel down a special pathway through your heart.

• The impulse starts in a small bundle of specialized cells called the SA node (sinoatrial node), in the right atrium. This node is known as the heart’s natural pacemaker. The electrical activity spreads through the walls of the atria and causes them to contract.
• A cluster of cells in the center of the heart between the atria and ventricles, the AV node (atrioventricular node) is like a gate that slows the electrical signal before it enters the ventricles. This delay gives the atria time to contract before the ventricles do.
• The His-Purkinje network is a pathway of fibers that sends the impulse to the muscular walls of the ventricles, causing them to contract.

At rest, a normal heart beats around 50 to 99 times a minute in an adult. Exercise, emotions, fever, and some medications can cause your heart to beat faster, sometimes to well over 100 beats per minute.

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The heart is the “engine”, the center and the sanctum of the human body. It was sung by great poets, studied by the best scientific minds. Today, science knows almost everything about the heart. But even the leading cardiologists of the world do not cease to be amazed at the perfection of his work.

The physiological properties of the heart are truly impressive. It is able to contract rhythmically without the influence of external stimuli. Impulses arise in the organ itself! This phenomenon is called automatism of the heart. Under the action of electrical, chemical and other stimuli on it, the excitation of the heart muscle (myocardium) occurs and, as a result, its contraction. During periods of excitation and contraction, the heart becomes nothing more than an electric generator: the tissues of the human body, having high conductivity, allow recording electrical potentials. Their recording is carried out using electrocardiography (ECG) – the most common and affordable method for diagnosing the work of the heart.

Anatomically, the heart is a hollow muscular organ. Its main function is to ensure uninterrupted blood flow through the vessels and, accordingly, the blood supply to all organs and systems of the human body. This task is difficult and requires incredible endurance. Despite its small size, the heart has it. In just one minute, it pumps five to six liters of blood. And in extreme conditions with heavy loads in 60 seconds, it is able to withstand a load of 30 liters!

The average weight of a heart is about 300 grams. Usually the size of this organ coincides with the volume of the clenched fist of its owner.

How is the heart arranged?

There are four chambers in the heart: the right and left atrium, and the right and left ventricles. Between themselves, the atria and ventricles are separated by septa and valves that allow blood to flow in only one direction. The atria store blood, and the ventricles, with the help of a strong muscle contraction, push it into the bloodstream.

is responsible for the rhythmic beat of the middle (muscular) layer of the heart – the myocardium.

Curiously, after each contraction, the myocardium enters a phase of relaxation – for only 0. 4 seconds. But if you count, then during the day our heart works 8 hours, and relaxes as much as 16! In 24 hours, it makes about 108,000 beats.

Of course, the heart has helpers. By pumping blood, it distributes it through the vessels. These hollow “tubes” permeate the entire human body. And it is through them that oxygen and nutrients are delivered to all organs.

So, together the heart and blood vessels are the human cardiovascular system .

Gradation of blood vessels:

Arteries and arterioles

They bring arterial scarlet blood enriched with oxygen and nutrients to the tissues and organs.

Capillaries

The smallest and thinnest vessels. Provide exchange of substances between blood and tissues.

Venules and veins

They play the role of “cleaners”: they collect venous blood throughout the body – poor in oxygen and containing metabolic products (it is darker in color due to the low oxygen content compared to arterial blood).

All vessels form two circles of blood circulation: large and small. Lesser vessels deliver venous blood to the lungs to enrich it with oxygen. And through vessels of the large circle , the heart pushes arterial blood to all organs and systems.
Including, about 20% of the pumped blood is involved in the own system of blood supply and nutrition of the heart (system of coronary vessels). This feature allows our “motor” to work for a very long time without failures.

What helps keep your heart healthy?

Go through life laughing, not forgetting about healthy food, sports and the balance of trace elements in the body – that’s all that is required of a person! The bursting “laughter from the heart” dilates blood vessels, and a large dose of oxygen enters the brain. In addition, having fun, we automatically lower the levels of stress hormones: cortisol and adrenaline, which have a devastating effect on the human cardiovascular system.

Smile to your heart!

Similar articles

Heart and vessels

The basis of the circulatory system is the heart, which, like a pump, pumps blood through the arteries, ensuring the delivery of oxygen and nutrients to all organs and tissues.
The heart is located in the chest along the projection of the sternum, somewhat to the left, and is a hollow muscular organ the size of a fist. The heart has 4 chambers separated by septa. Between left atrium
and the left ventricle, as well as the right atrium and right ventricle, there are openings with valves that regulate the direction of blood flow from the atria to the ventricles.
Blood circulation occurs through the systemic and pulmonary circulation. Blood is collected from all organs and tissues and enters the right atrium through the veins. From the right atrium, through the corresponding opening, venous blood enters the right ventricle. Both of these right reservoirs (atrium and ventricle) are also called the right heart (“venous”).
The pulmonary circulation begins in the right ventricle. From the right ventricle, due to the contraction of its muscular wall, dark, oxygen-poor and rich in carbon dioxide blood is pushed into the pulmonary artery and enters the lungs through it. There it enters small arteries and capillaries, is purified from carbon dioxide by diffusion and enriched with oxygen, acquires a bright red color and is already called arterial blood. Through the four pulmonary veins, arterial blood enters the left atrium, and this completes the pulmonary circulation.
Considering that the left cavities of the heart (atrium and ventricle) or the left heart are already filled with arterial blood, the left heart is called “arterial”.
The systemic circulation begins in the left atrium. From the left atrium, arterial blood enters the left ventricle, which is an even more powerful pump than the right ventricle. Contracting, the left ventricle pushes blood into the aorta and its branches, through which it enters all organs and tissues, down to the smallest capillaries. Having given oxygen to the tissues and taking away carbon dioxide from them, the blood again becomes venous. The venous capillaries connect with each other gradually into larger veins, which, in turn, form two wide ones: the superior and inferior vena cava. The superior vena cava collects blood from the head, neck, upper limbs, and trunk walls, while the inferior vena cava collects blood from the lower limbs, abdominal organs, and pelvic region. Both vena cava carry blood to the right atrium, where the systemic circulation ends.

Thus, 2 vicious circles of blood circulation are obtained, which are interconnected by the motor of the human body – the heart.
So, the systemic circulation begins in the left ventricle of the heart and ends in the right atrium. Its function is to supply all organs and tissues with nutrients and oxygen.
The pulmonary circulation starts from the right ventricle and ends in the left atrium. Its function is to enrich the blood with oxygen in the lungs.
The heart muscle, constantly performing gigantic work, itself needs nutrition and oxygen. Blood enters the heart through vessels that branch directly from the aorta and surround the heart like a crown or crown, which is why they are called coronary or coronary arteries.

The movement of blood through the vessels.

The heart does a lot of work. So, in one minute it pumps 4.5-5 liters of blood in only one direction. The movement of blood is provided by valves located between the atria and ventricles, between the left ventricle and aorta, pulmonary vessels and the right atrium. The speed of blood movement through the vessels depends on their diameter: if in the aorta the blood moves at a high speed, then in the capillaries this speed is minimal.
When the cardiovascular system is damaged by an atherosclerotic, inflammatory or degenerative process, both general and local circulatory disorders can be observed. An example of common circulatory disorders is heart failure with shortness of breath, palpitations, cough, cyanosis of the skin and edema. An example of local circulatory disorders, when the blood supply to any organ suffers, is a heart attack (of the heart, lung or kidneys), gangrene of a limb. But since the circulatory system functions as a whole, even local circulatory disorders in any organ eventually affect the entire system.
The activity of the heart is regulated by the central nervous system. In addition, the heart has its own intracardiac regulatory mechanisms that contribute to the rhythmic contraction (systole phase) and relaxation (diastole phase) of the heart.
In an adult, the number of heartbeats per minute normally ranges from 60 to 80 beats; in athletes, the heart works more economically. They have a heart rate of 40-50 beats per minute.

Arteries in our body

Before talking about atherosclerosis, let us recall the anatomical features of the arteries.
Arteries are cylindrical elastic tubes of various diameters. The walls of arteries are much thicker than those of veins, the vessels that carry blood back to the heart. This difference in the thickness of the vessels is not accidental and is due to the fact that the blood pressure in the arteries is much greater than in the veins.
The wall of the arteries consists of three layers: outer, middle and inner. The outer layer or serosa is a framework of connective tissue; the middle (muscle) layer consists of smooth muscle fibers; the inner layer (intima) is lined with a single layer of cells and is called the endothelium. It is the endothelium, or rather its damage or dysfunction, that plays a major role in the development of atherosclerosis. However, we will talk about this later.
The lumen of the arteries can change as a result of contraction or relaxation of the smooth muscle fibers of the middle layer. Expansion of blood vessels (for example, in conditions of heat) contributes to an increase in blood flow and a more intensive metabolism, and vice versa, their narrowing (in conditions of low temperatures) slows down these processes in the body. If for some reason the vessels are constantly narrowed, then the organs and tissues receive little blood, and hence oxygen. Over time, this leads to disruption of the functioning of those organs and tissues that are powered by narrowed arteries.

Vascular changes in atherosclerosis

Atherosclerosis (from the Greek words “ater” – gruel and “sclerosis” – hardening), exactly in accordance with the name, is a process of accumulation of soft deposits of lipids (fats, fat-like substances, primarily cholesterol) on the walls of the arteries.

It has been established that atherosclerosis develops in response to damage to the endothelium (the inner lining of blood vessels).

Damage or dysfunction of the endothelium can be caused by a number of reasons, in particular, smoking, a significant increase in blood lipids, high blood pressure, acute or chronic psycho-emotional stress, viral or bacterial infection.
Following damage to the endothelium, penetration into the arterial wall of fats, fat-like substances, and cholesterol begins. Leukocytes, or rather their special varieties, monocytes and macrophages, also rush here from the blood. This is the beginning of the formation of atherosclerotic plaque. The “slurry” formed on the wall of the artery is covered with a thin connective tissue capsule consisting of fibrin threads. Such atherosclerotic plaque is called young. Over time, as the atherosclerotic process progresses, calcium begins to accumulate in the plaques, fibrous and connective tissue grows. The plaque is covered with a thick capsule (this is a formed plaque), increases in size and significantly narrows the lumen of the artery. Often several plaques are formed, they merge with each other, further narrowing the lumen of the vessel.
Due to the narrowing of the lumen of the vessel, the organ supplied by it does not receive the necessary amount of oxygen and chronic ischemia occurs (from the Greek words “ische” – I delay and “hemo” – blood). So, with the narrowing of one or more coronary arteries, chronic myocardial ischemia (chronic coronary heart disease) occurs.

Acute ischemia (acute vascular insufficiency) develops differently. The fact is that the body produces special enzymes that “corrode” the connective tissue membrane of an atherosclerotic plaque from the edges, reaching its soft, mushy core. When the plaque capsule is opened, this mass enters the bloodstream. An open wound on the capsule of an ulcerated plaque is covered with clumped platelets. A blood clot is gradually formed – a thrombus, which bulges into the lumen of the vessel, sharply narrowing it.
A thrombus can break away from the vessel wall and, moving with the blood flow, clog a smaller vessel, creating acute local vascular insufficiency and stopping tissue nutrition, which leads to tissue necrosis (death). For example, when one of the coronary arteries of the heart is blocked, myocardial infarction occurs, and when thrombosis of the femoral artery or the artery of the lower leg, necrosis of the foot (gangrene) occurs.
Atherosclerosis can totally affect the aorta and its branches, but arteries of various calibers are more often affected, and not all over, but in separate areas. Atherosclerotic plaques “like” to form in places of bends and branches of arteries, which are especially numerous in vital organs. Thus, the coronary arteries of the heart, the vessels of the brain, the abdominal aorta and its branches that supply blood to the abdominal organs, kidneys, pelvic organs, and lower limbs are most susceptible to atherosclerosis.
Often, atherosclerosis initially favors one organ. For example, with damage to the coronary arteries, coronary heart disease develops, with atherosclerosis of the cerebral arteries – ischemic brain disease up to a stroke. When atherosclerotic plaques narrow the iliac or femoral vessels, obliterating atherosclerosis of the vessels of the lower extremities occurs. If the renal vessels are affected by atherosclerosis, then hypertension may develop with a predominant increase in the “lower” numbers of blood pressure. Depending on the localization of the affected vessels, clinical manifestations of atherosclerosis of one or another vital organ are formed.