How does the human heart work. What are the main components of the cardiovascular system. How does blood circulation occur in the body. What role do heart valves play in cardiac function. How does the heart’s electrical system operate. What factors influence blood pressure. What are common cardiovascular diseases and their causes.

The Heart: Your Body’s Vital Pump

The heart is a remarkable organ that plays a crucial role in sustaining life. Located slightly to the left in the middle of your chest, this fist-sized muscle works tirelessly to pump blood throughout your body. But how exactly does it function? Let’s delve into the intricate workings of this vital organ.

Size and Location

How big is the human heart? The heart is approximately the size of a clenched fist, weighing between 8 to 12 ounces (230 to 340 grams) in adults. Its location is central to its function, positioned in the chest cavity between the lungs, with about two-thirds of its mass to the left of the body’s midline.

The Heart’s Layers

The heart is composed of three main layers of tissue:

• Epicardium: The outermost layer
• Myocardium: The middle layer, consisting of cardiac muscle
• Endocardium: The innermost layer

These layers are encased in a protective sac called the pericardium, which helps anchor the heart in place and allows it to function smoothly within the chest cavity.

Chambers of the Heart

How many chambers does the heart have? The heart consists of four chambers:

1. Right atrium
2. Right ventricle
3. Left atrium
4. Left ventricle

The atria are the smaller, upper chambers that receive blood, while the ventricles are the larger, lower chambers responsible for pumping blood out of the heart. These chambers are separated by a muscular wall called the septum, which prevents the mixing of oxygenated and deoxygenated blood.

The Circulatory System: Your Body’s Highway

The heart is the centerpiece of the circulatory system, also known as the cardiovascular system. This complex network is responsible for transporting oxygen, nutrients, hormones, and waste products throughout the body.

Components of the Circulatory System

What are the main components of the circulatory system? The circulatory system consists of:

• The heart
• Blood vessels (arteries, veins, and capillaries)
• Blood

Each of these components plays a vital role in maintaining the body’s homeostasis and ensuring that all tissues receive the oxygen and nutrients they need to function properly.

The Journey of Blood

How does blood circulate through the body? The circulation of blood is a continuous process that can be simplified into two main circuits:

1. Pulmonary circulation: Blood flows from the right side of the heart to the lungs and back to the left side of the heart.
2. Systemic circulation: Blood flows from the left side of the heart to the rest of the body and back to the right side of the heart.

This efficient system ensures that oxygenated blood is distributed to all parts of the body and deoxygenated blood is returned to the heart for reoxygenation in the lungs.

Blood Vessels: The Body’s Transport Network

Blood vessels form an intricate network that allows blood to reach every part of the body. There are three main types of blood vessels:

Arteries

What is the function of arteries? Arteries carry oxygen-rich blood away from the heart to the body’s tissues. They have thick, muscular walls to withstand the high pressure of blood pumped by the heart. As arteries move further from the heart, they branch into smaller vessels called arterioles.

Capillaries

Capillaries are the smallest blood vessels in the body. Their thin walls allow for the exchange of oxygen, nutrients, and waste products between the blood and surrounding tissues. This exchange is crucial for cellular metabolism and overall body function.

Veins

What role do veins play in circulation? Veins carry deoxygenated blood from the body’s tissues back to the heart. Unlike arteries, veins have thinner walls and contain valves that prevent blood from flowing backward. As veins approach the heart, they merge into larger vessels, ultimately forming the vena cava, which empties into the right atrium.

The Heart’s Valves: Gatekeepers of Blood Flow

The heart contains four valves that ensure blood flows in the correct direction through its chambers. These valves open and close in response to pressure changes within the heart.

Types of Heart Valves

What are the four valves of the heart? The heart’s valves are:

• Tricuspid valve: Between the right atrium and right ventricle
• Pulmonary valve: Between the right ventricle and pulmonary artery
• Mitral valve: Between the left atrium and left ventricle
• Aortic valve: Between the left ventricle and aorta

These valves work in perfect synchronization to maintain the unidirectional flow of blood through the heart.

Valve Function

How do heart valves work? Heart valves function like one-way gates, opening to allow blood to flow through and closing to prevent backflow. This mechanism ensures that blood moves efficiently through the heart’s chambers and into the circulatory system.

The Heart’s Electrical System: The Rhythm of Life

The heart’s ability to beat rhythmically and continuously is due to its intricate electrical system. This system generates and conducts electrical impulses that coordinate the heart’s contractions.

Components of the Cardiac Conduction System

What are the key components of the heart’s electrical system? The main elements include:

• Sinoatrial (SA) node: The heart’s natural pacemaker
• Atrioventricular (AV) node: Delays the electrical signal before it reaches the ventricles
• Bundle of His: Conducts the impulse to the ventricles
• Left and right bundle branches: Distribute the impulse throughout the ventricles
• Purkinje fibers: The final branching network that stimulates individual cardiac muscle fibers

This system ensures that the heart’s chambers contract in the correct sequence and with proper timing.

The Cardiac Cycle

How does the cardiac cycle work? The cardiac cycle refers to the sequence of events that occur during one heartbeat. It consists of two main phases:

1. Systole: The contraction phase, where blood is ejected from the heart
2. Diastole: The relaxation phase, where the heart chambers fill with blood

These phases are coordinated by the heart’s electrical system, resulting in the rhythmic beating we associate with a healthy heart.

Blood Pressure: The Force of Life

Blood pressure is a crucial measure of cardiovascular health, representing the force exerted by blood against the walls of arteries as it flows through them.

Factors Influencing Blood Pressure

What determines blood pressure? Blood pressure is influenced by several factors:

• The heart’s pumping action
• The elasticity and diameter of blood vessels
• Blood volume and viscosity
• Hormonal and nervous system regulation

Understanding these factors is essential for maintaining healthy blood pressure levels and preventing cardiovascular diseases.

Measuring Blood Pressure

How is blood pressure measured? Blood pressure is typically recorded as two numbers:

1. Systolic pressure: The pressure when the heart contracts
2. Diastolic pressure: The pressure when the heart relaxes between beats

A normal blood pressure reading for adults is generally considered to be below 120/80 mmHg. Regular monitoring of blood pressure is crucial for early detection and management of hypertension and other cardiovascular conditions.

Cardiovascular Health: Challenges and Disorders

While the cardiovascular system is remarkably resilient, it can be susceptible to various disorders and diseases. Understanding these conditions is crucial for maintaining heart health and preventing complications.

Common Cardiovascular Diseases

What are some prevalent cardiovascular diseases? Some of the most common heart and circulatory system disorders include:

• Coronary artery disease (CAD)
• Heart attack (myocardial infarction)
• Stroke
• Heart failure
• Arrhythmias
• Valvular heart disease
• Hypertension (high blood pressure)

Each of these conditions can have serious implications for overall health and quality of life.

Risk Factors and Prevention

How can cardiovascular diseases be prevented? Many cardiovascular diseases share common risk factors, some of which are modifiable. Key preventive measures include:

1. Maintaining a healthy diet rich in fruits, vegetables, and whole grains
2. Engaging in regular physical activity
3. Managing stress through relaxation techniques and adequate sleep
4. Avoiding tobacco use and excessive alcohol consumption
5. Controlling other health conditions such as diabetes and high cholesterol
6. Regular health check-ups and screenings

By addressing these factors, individuals can significantly reduce their risk of developing cardiovascular diseases and improve their overall heart health.

Understanding the intricacies of the cardiovascular system is crucial for appreciating the importance of heart health. From the heart’s structure and function to the complex network of blood vessels and the delicate balance of blood pressure, each component plays a vital role in maintaining our well-being. By staying informed about cardiovascular health and taking proactive steps to protect our hearts, we can ensure that this remarkable organ continues to pump life through our bodies for years to come.

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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European Society of Cardiology (ESC) guidelines for the diagnosis and treatment of heart failure

What patients need to know

This European Society of Cardiology (ESC) patient guide is a summary of the most current evidence-based recommendations for the diagnosis and treatment of heart failure.

In particular, it is designed to help patients understand:

• what are the main types of heart failure;
• what medicines are used to treat heart failure;
• which devices can be used;
• why full rehabilitation is important;
• how important is treatment by medical specialists of different profiles;
• how important it is to take care of yourself and control your condition.

To learn more

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These videos explain how a healthy heart works, what happens in heart failure, and how various treatments can help improve your health

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heartfailurematters.org — website of the European Society of Cardiology

The website heartfailurematters.org was created under the direction of the Association of Heart Failure Specialists of the European Society of Cardiology (ESC). ESC is a world leader in the discovery and dissemination of advanced methods of cardiovascular medicine. Our members and decision makers are medical professionals who volunteer their time and knowledge as cardiologists in Europe and beyond.

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. This blood then returns to the heart through the pulmonary veins.

Vienna

Blood with carbon dioxide and metabolic products from the capillaries first enters the veins, and through them moves to the heart.