How the Heart Works: A Simple Guide to Your Body’s Remarkable Pump
How the Heart Works: Chambers, Valves and Blood Flow
You rarely notice your heart when it is doing its job well.
Even while you are sitting quietly, this fist-sized muscle is filling, squeezing, opening and closing valves, and adjusting its pace to match what your body needs.
The heart is often described as a pump, but that is only part of the story. It is really two pumps working side by side, guided by its own electrical system and protected by four one-way valves.
Once you understand those basic parts, terms such as blood pressure, heart rhythm, heart attack and cardiac arrest become much easier to follow.
What Is the Heart?
Your heart is a muscular organ located inside your rib cage, behind your breastbone and slightly to the left.
It is about the size of your clenched fist and sits at the centre of your circulatory system. This system includes your blood and the network of arteries, veins and tiny capillaries that carry it throughout your body.
The heart’s main job is to keep blood moving.
That blood delivers oxygen and nutrients to your organs and tissues. It also carries carbon dioxide back to your lungs, where it can be breathed out.
Is the Heart One Pump or Two?
A useful way to picture the heart is as two pumps joined together.
The right side receives blood returning from the body and sends it to the lungs.
The left side receives oxygen-rich blood from the lungs and sends it to the rest of the body.
These two sides work in sequence. The right side handles the lung circuit, while the left side produces the pressure needed to move blood from your head to your toes.
What Are the Four Chambers of the Heart?
The heart has four hollow chambers.
The two upper chambers are called the atria. They mainly receive blood.
The two lower chambers are called the ventricles. They do most of the pumping.
• Right atrium: Receives oxygen-poor blood returning from the body.
• Right ventricle: Pumps that blood to the lungs to collect oxygen.
• Left atrium: Receives oxygen-rich blood returning from the lungs.
• Left ventricle: Pumps oxygen-rich blood into the aorta and around the body.
The left ventricle has the biggest pumping job because it must generate enough pressure to send blood throughout the entire body.
What Do the Heart Valves Do?
If the chambers are rooms, the valves are one-way doors.
They open to let blood move forward and close to stop it flowing backwards. The heart has four valves:
• 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
The familiar “lub-dub” sound of a heartbeat comes largely from these valves closing.
The “lub” occurs when the valves between the atria and ventricles close. The “dub” follows when the pulmonary and aortic valves close after the ventricles have pushed blood out.
How Does Blood Flow Through the Heart?
The full journey may sound complicated, but the basic route is simple:
Body → right side of the heart → lungs → left side of the heart → body
Here is the journey step by step:
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Oxygen-poor blood returns from the body through two large veins called the venae cavae.
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It enters the right atrium and passes through the tricuspid valve into the right ventricle.
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The right ventricle pumps it through the pulmonary valve and into the pulmonary artery.
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The pulmonary artery carries the blood to the lungs, where carbon dioxide is released and oxygen is collected.
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Oxygen-rich blood returns through the pulmonary veins and enters the left atrium.
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It passes through the mitral valve into the left ventricle.
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The left ventricle pumps it through the aortic valve and into the aorta, the body’s largest artery.
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The blood travels through progressively smaller vessels until oxygen and nutrients reach the body’s tissues. It then begins the return journey through the veins.
This cycle repeats continuously.
One useful detail is that arteries are named because they carry blood away from the heart, while veins carry blood towards it. That is why the pulmonary artery carries oxygen-poor blood and the pulmonary veins carry oxygen-rich blood—the opposite of what many people expect.
How Does the Heart Know When to Beat?
Your heart has its own electrical conduction system.
Each normal heartbeat begins in a small group of specialised cells called the sinoatrial node, or SA node, in the right atrium. It is often described as the heart’s natural pacemaker.
The electrical signal then follows a carefully timed route:
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The signal spreads across the atria, causing them to contract and push blood into the ventricles.
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It reaches the atrioventricular node, or AV node, where it pauses briefly. This gives the ventricles time to fill.
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The signal travels through the lower part of the heart, causing the ventricles to contract and pump blood to the lungs and body.
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The heart relaxes, refills and begins the cycle again.
A resting heart rate between 60 and 100 beats per minute is commonly considered within the usual adult range. Exercise, sleep, stress, fitness, medicines and health conditions can all affect that number, so a single reading does not tell the whole story.
How Does the Heart Get Its Own Oxygen?
The heart moves oxygen-rich blood around the body, but its own muscle also needs a reliable oxygen supply.
That supply comes through the coronary arteries, which branch from the aorta and run across the surface of the heart.
When a coronary artery becomes narrowed, the heart muscle may receive less blood during activity, sometimes causing angina. If blood flow is suddenly blocked, part of the heart muscle can be injured in a heart attack.
Atherosclerosis is one common reason coronary arteries can narrow over time. Read more about how atherosclerosis develops and why its risk factors matter.
How Does Blood Pressure Fit In?
Every time the ventricles squeeze, they create pressure that moves blood through the arteries.
Blood pressure is written as two numbers:
• Systolic pressure: The pressure when the ventricles contract and pump blood out
• Diastolic pressure: The pressure while the heart relaxes and refills between beats
Your blood pressure changes during the day and can be influenced by activity, stress, sleep, pain, medicines and other factors.
Learn more about what blood pressure numbers mean and why they matter for your heart.
What Is the Difference Between a Heart Attack and Cardiac Arrest?
These terms are often used as though they mean the same thing, but they describe different emergencies.
A heart attack is usually a blood-flow problem. A blocked coronary artery prevents part of the heart muscle from receiving enough oxygen. The heart will often continue beating during a heart attack.
Cardiac arrest is an electrical and pumping emergency. The heart suddenly stops pumping blood effectively, and the person becomes unresponsive and does not breathe normally.
A heart attack can sometimes trigger cardiac arrest, but the two are not interchangeable. Our guide to heart attack versus cardiac arrest explains the distinction in more detail.
What Changes in the Heart as You Get Older?
The heart does not simply “wear out” at a certain age. However, normal ageing can change how the heart and blood vessels respond.
Arteries may become stiffer, which can contribute to higher blood pressure. The heart may also be less able to increase its rate during strenuous activity or stress than it was in younger years.
Age can also increase the likelihood of conditions involving the coronary arteries, valves or heart rhythm. That does not mean new symptoms should automatically be dismissed as “just getting older”.
For readers in their 50s and beyond, it is particularly useful to know your blood pressure, cholesterol, blood sugar, smoking status and family history. A cardiovascular risk assessment with a doctor or qualified healthcare professional can consider these factors together and estimate your overall risk. They can advise whether an assessment is appropriate for you and how often your health checks should occur.
How Can Doctors Check How Well the Heart Is Working?
Not everyone needs every heart test. The right test depends on your symptoms, medical history and risk factors.
Common checks include:
• Pulse and blood pressure: Provide basic information about heart rate, rhythm and pressure in the arteries
• Electrocardiogram, or ECG: Records the heart’s electrical activity
• Echocardiogram: Uses ultrasound to show the chambers, valves and pumping action
• Stress test: Assesses how the heart responds to physical activity or medicine-induced stress
• Blood tests: May check cholesterol, blood sugar and other markers that influence cardiovascular risk
Taking a written list of symptoms, medicines and family history can make an appointment more useful. AtheroCare’s heart health checklist of questions to ask your doctor can help you prepare.
What Can Help Support the Heart’s Work?
The heart works automatically, but many everyday choices affect the conditions under which it has to work.
Helpful steps can include:
• Staying physically active at a level that is suitable for you
• Eating a varied, balanced diet
• Not smoking or vaping
• Limiting alcohol
• Getting enough sleep
• Managing blood pressure, cholesterol and blood sugar with professional guidance
• Taking prescribed medicines as directed
• Attending recommended health checks
People with an existing condition, new symptoms or a long break from exercise should speak with a doctor or qualified health professional before making major changes to their activity routine.
When Should You Seek Emergency Medical Help?
Some symptoms may signal a heart attack or another serious cardiovascular emergency. Seek emergency medical help immediately if you or someone else experiences possible warning signs such as:
• Pressure, squeezing, tightness, heaviness, pain or discomfort in the centre of the chest
• Pain or discomfort in one or both arms, the shoulders, back, neck or jaw
• Shortness of breath
• A cold sweat
• Feeling weak, light-headed or faint
• Nausea or vomiting
• Unusual or unexplained tiredness
Symptoms can be mild, may come and go, and do not always include chest pain. Do not wait for them to become severe or assume they will pass. Contact the emergency medical service for your location and follow the operator’s instructions. The World Health Organization advises seeking medical care immediately when possible heart attack symptoms occur.
If someone collapses, is unresponsive and is not breathing normally, contact local emergency medical services immediately. Begin CPR, follow the emergency dispatcher’s instructions and use an automated external defibrillator (AED) as soon as one is available. Follow the prompts given by the AED.
Read more about how to recognise a possible heart attack and what to do next.
Questions to Ask Your Doctor
You may wish to ask:
• Is my blood pressure in a healthy range for me?
• Would a cardiovascular risk assessment be appropriate for me?
• Is my resting pulse or heart rhythm a concern?
• Could my symptoms require an ECG, echocardiogram or another test?
• How does my family history affect my risk?
• What type and amount of physical activity is suitable for me?
• Could any of my medicines affect my heart rate or blood pressure?
The Bottom Line
The heart is a muscular double pump with four chambers, four one-way valves, its own electrical system and its own blood supply.
The right side sends oxygen-poor blood to the lungs. The left side sends oxygen-rich blood to the body. Electrical signals keep the chambers contracting in the correct order, while the valves keep blood moving forward.
Understanding this basic system can make heart-health information much less mysterious. It can also help you see why blood pressure, heart rhythm, coronary arteries and regular health checks all matter—especially as you move through your 50s and beyond.
Related AtheroCare Reading
What Is Blood Pressure and Why Does It Matter for Your Heart Health?
Learn what systolic and diastolic readings mean and why blood pressure is an important part of cardiovascular health.
Heart Attack vs Cardiac Arrest
Understand the difference between a blood-flow emergency and an electrical emergency.
Understanding Atherosclerosis: Causes, Symptoms and Risk Factors
Learn how changes inside the arteries can affect blood flow and cardiovascular health.
How to Spot a Heart Attack—and What to Do Next
Review common warning signs and the steps to take in an emergency.
What to Ask Your Doctor: A Heart Health Checklist
Prepare useful questions about your symptoms, risk factors, tests and medicines.
References
Heart Foundation: How Your Heart Works
National Heart, Lung, and Blood Institute: How Blood Flows Through the Heart
National Heart, Lung, and Blood Institute: How the Heart Beats
National Institute on Aging: Heart Health and Aging
Heart Foundation: Medical Tests for Heart Disease
World Health Organization: Cardiovascular Diseases
Centers for Disease Control and Prevention: Heart Attack Symptoms, Risk and Recovery
American Heart Association: Treatment of Cardiac Arrest
Medical Disclaimer
This article is provided for general information and education only. It is not intended to provide medical advice, diagnosis or treatment.
Always speak with a qualified healthcare professional about symptoms, medicines, test results and your personal cardiovascular risk. Do not begin, stop or change any treatment based only on information in this article.
