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

How your heart works – Heart and circulatory system – British Heart Foundation

The human heart works like a pump sending blood around your body to keep you alive.

It’s a muscle, about the size of your fist, in the middle of your chest tilted slightly to the left.

What is the function of the human heart?

Each day, your heart beats around 100,000 times. This continuously pumps about five litres (eight pints) of blood around your body through a network of blood vessels called your circulatory system. This blood delivers oxygen and nutrients to all parts of your body to help your organs and muscles work properly. Your blood also carries away unwanted carbon dioxide and waste products.

What is the structure of the human heart?

Your heart has a left side and a right side, they are separated by a thin muscular wall called the Septum. Both sides of your heart have an upper chamber and a lower chamber.

• the upper chambers are called the left atrium and the right atrium (or the atria)
• the lower chambers are called the left ventricle and the right ventricle.

The right side of your heart receives the de-oxygenated blood that has just travelled round your body. It pumps the blood to your lungs to collect a fresh supply of oxygen. The left side of your heart pumps the re-oxygenated blood round your body again.

Your heart muscle is made up of three layers of tissue:

• Pericardium – a thin, outer lining that protects and surrounds your heart.
• Myocardium – a thick, muscular middle layer that contracts and relaxes to pump blood around of your heart.
• Endocardium – a thin, inner layer that makes up the lining of the four chambers and the valves in your heart.

What does the heart’s electrical system do?

Your heart’s electrical system tells your heart when to contract and when to relax to keep your blood pumping regularly. The instructions to contract and relax are carried by electrical signals.

The electrical signals are sent from the sinus node which is known as your heart’s natural pacemaker. Usually, the sinus node will send the electrical signals at a steady pace, but the pace can change depending on your emotions and if you are active or resting – this is your heart rate.

How does blood flow around the heart and the body?

Your heart is linked to the rest of the circulatory system with blood vessels called arteries and veins.

• your arteries deliver oxygen-rich blood from the heart to other areas of your body
• your veins return the de-oxygenated blood from your organs back to your heart
• your arteries and veins are connected by even smaller blood vessels called capillaries.

Your blood flows around your heart and the rest of your body in one direction, like a one-way traffic system. Your heart valves control the direction of your blood flow, they act like doors that open and close with every heartbeat. There are four valves in your heart, they are:

• the tricuspid valve and the pulmonary valve on the right side of the heart
• the mitral valve and the aortic valve on the left side of your heart.

Like the rest of your body, your heart needs to be supplied with oxygen-rich blood to work properly too. The coronary arteries are the arteries responsible for supplying the heart with oxygenated blood. The coronary arteries are spread across the outside of the heart to deliver the blood.

How do your heart and lungs add oxygen to your blood?

Your blood flows through your heart and your lungs to become re-oxygenated before being pumped to the rest of your body. Oxygen is added to your blood in four main steps, they are:

• The right atrium receives the low-oxygen blood that has just travelled round the body. The right atrium pumps the blood to the right ventricle.
• The right ventricle pumps the low-oxygen blood to the lungs to pick up a fresh supply of oxygen.
• The left atrium receives to high-oxygen blood from the lungs and pumps it to the left ventricle.
• The left ventricle pumps the high-oxygen blood to the rest of the body.

What are heart and circulatory diseases?

Sometimes the heart and circulatory system don’t work like they should, this can cause heart and circulatory diseases (also called cardiovascular diseases). We fund research into these conditions and their risk factors, including:

• coronary heart disease (heart attack and angina)
• congenital heart disease
• inherited heart conditions
• stroke
• vascular dementia
• diabetes.

What causes your heart and circulatory system to go wrong?

Problems with your heart and circulatory system, including heart attack or a stroke, are usually caused by a gradual build-up of fatty material (called atheroma) in the arteries around the heart and in the arteries that supply blood to your brain.

The fatty material lines the walls of heart’s coronary arteries making the space for blood to flow narrower. When the arteries become narrowed and the blood flow is restricted, the arteries can’t deliver enough blood to the heart and the brain, which can cause heart and circulatory diseases.

What puts me at risk of heart and circulatory disease?

Many heart and circulatory diseases share the same risk factors including:

• poorly managed diabetes
• high blood pressure
• high cholesterol
• being overweight or obese
• smoking
• drinking too much alcohol.

Heart and circulatory diseases can be worrying but the good news is that there are lots of things you can do to reduce your risk of developing heart and circulatory diseases now.

Check your heart age

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Page last reviewed: August 2021
Next review due: August 2024

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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.
Atherosclerosis in its development is not like any other disease, since the first signs of it appear in early childhood. So, at the age of six months, fatty spots and stripes appear on the inner wall of the vessels in some babies. In the process of growth, a significant part of these spots resolves and only a few remain. If you do not engage in prevention, then by the age of 35-50 in men and somewhat later in women, clinical signs of atherosclerosis appear in the form of coronary heart disease, ischemic disease of the brain and other organs. The resulting disease requires many years, and in fact lifelong treatment. Meanwhile, in medicine it has long been proven that serious diseases, including atherosclerosis, are better and easier to prevent than to treat later for many, many years. In order to prevent atherosclerosis, you need to know everything about the substrate of atherosclerotic plaques – cholesterol and its assistants – lipoproteins.

The cardiovascular system and what it includes

The cardiovascular system is one of the most important systems of the body that ensures its vital activity. The cardiovascular system provides blood circulation in the human body. Blood with oxygen, hormones and nutrients is carried through the vessels throughout the body. Along the way, it shares these compounds with all organs and tissues. Then he takes everything that is left of the metabolism for further disposal.

Heart

Blood circulates in the body thanks to the heart. It rhythmically contracts like a pump, pumping blood through the blood vessels and providing all organs and tissues with oxygen and nutrients. The heart is a living motor, a tireless worker, in one minute the heart pumps about 5 liters of blood through the body, in an hour – 300 liters, in a day it accumulates 7,000 liters.

Circulatory circuits

Blood flowing through the cardiovascular system can be compared to an athlete who runs different distances. When it passes through the small (pulmonary) circulation, it is a sprint. And the big circle is already a marathon. These circles were described by the Englishman William Harvey in 1628. During the great circle, the blood is carried throughout the body, not forgetting to provide it with oxygen and take away carbon dioxide. During this “run” arterial blood becomes venous.

The pulmonary circulation is responsible for the flow of blood to the lungs, where the blood gives off carbon dioxide and is enriched with oxygen. Blood from the pulmonary circulation returns to the left atrium. A large circle of blood circulation, starting in the left ventricle, ensures the transport of blood throughout the body. Oxygenated blood is pumped by the left ventricle into the aorta and its many branches – the various arteries. Then it enters the capillary vessels of organs and tissues, where oxygen from the blood is exchanged for carbon dioxide. The systemic circulation ends in small veins that merge into two large veins (vena cava) and return blood to the right atrium. The superior vena cava drains blood from the head, neck, and upper extremities, and the inferior vena cava drains blood from the trunk and lower extremities.

Blood vessels

Blood vessels are elastic tubular formations in the human body, through which the force of a rhythmically contracting heart or pulsating vessel moves blood through the body. Through the arteries, blood runs from the heart to the organs, through the veins it returns to the heart, and the smallest vessels – capillaries – bring blood to the tissues.

arteries

No cell can do without nutrients and oxygen. They are delivered by arteries. They carry oxygen-rich blood throughout the body. When you breathe in, oxygen enters your lungs. where further oxygen delivery throughout the body begins. First to the heart, then through the systemic circulation to all parts of the body. There, the blood exchanges oxygen for carbon dioxide and then returns to the heart. The heart pumps it back to the lungs, which take in carbon dioxide and give out oxygen, and so on endlessly. And then there are the pulmonary arteries of the pulmonary circulation, they are located in the lungs and through them the blood, poor in oxygen and rich in carbon dioxide, enters the lungs, where gas exchange occurs.