How Your Heart Works
Your heart is more than a pump.
Learn how its chambers, valves, blood vessels, and electrical system work together to keep blood moving through your body.
Your heart works around the clock—beating, pumping, and adjusting to what your body needs.
When you're sleeping, exercising, working, laughing, or simply sitting still, your heart is continuously moving blood between your lungs and the rest of your body.
But how does it actually do that?
Inside your heart is a remarkably coordinated system of chambers, valves, blood vessels, and electrical signals. Each has a different job, but they have to work together.
Understanding how a healthy heart works makes it much easier to understand what happens when something goes wrong.
BUTTON: Meet Your Heart ↓
Meet Your Heart
Your Heart Has One Big Job
At its simplest, your heart is a muscular pump.
Its job is to keep blood circulating so your body's tissues receive the oxygen and nutrients they need—and so blood can return to the lungs to pick up more oxygen.
But the heart doesn't accomplish this with one big squeeze.
It relies on several parts working together.
THE PUMP
Heart muscle creates the force.
THE ROOMS
Four chambers receive and move blood.
THE DOORS
Four valves keep blood moving in the right direction.
THE ELECTRICAL SYSTEM
Coordinates when the heart beats.
One heart. Different parts. One coordinated system.
Four Chambers. Two Sides. One Continuous Flow.
Your heart has four chambers—two on the right and two on the left.
The upper chambers are called the atria. They receive blood.
The lower chambers are called the ventricles. They pump blood out.
But there's an even simpler way to understand what's happening.
RIGHT SIDE
Sends Blood to the Lungs
Blood returning from your body is low in oxygen. The right side of your heart receives that blood and pumps it to your lungs, where it picks up oxygen.
Right Atrium → Right Ventricle → Lungs
LEFT SIDE
Sends Oxygen-Rich Blood to the Body
Blood returns from your lungs filled with oxygen. The left side of your heart receives it and pumps it out to your brain, kidneys, muscles, and the rest of your body.
Left Atrium → Left Ventricle → Body
Why Is the Left Ventricle So Muscular?
Because it has the biggest pumping job.
The right ventricle only needs to send blood to the nearby lungs. The left ventricle has to generate enough pressure to send blood throughout your entire body.
That's why its muscular wall is normally thicker.
The structure of your heart reflects the work it has to do.
VISUAL: Simplified four-chamber heart — Right Atrium • Right Ventricle • Left Atrium • Left Ventricle
Your Heart Has Four One-Way Doors
As blood moves through your heart, it needs to keep moving forward.
That's the job of your heart valves.
Think of them as one-way doors. They open to allow blood to move forward and then close to help prevent blood from flowing backward.
Your heart has four valves:
TRICUSPID VALVE
Between the right atrium and right ventricle
PULMONIC VALVE
Between the right ventricle and the artery leading to the lungs
MITRAL VALVE
Between the left atrium and left ventricle
AORTIC VALVE
Between the left ventricle and the aorta—the major artery carrying blood to your body
What Makes the “Lub-Dub”?
When your healthcare professional listens to your heart with a stethoscope, the familiar:
“Lub-dub. Lub-dub.”
comes primarily from the closing of your heart valves during the cardiac cycle.
Those sounds help your healthcare professional listen to what's happening as your heart moves blood.
When a Valve Doesn't Work Normally
Sometimes a valve becomes too narrow and doesn't open fully. This is called stenosis.
Or a valve may not close completely, allowing some blood to leak backward. This is called regurgitation.
Abnormal blood flow across a valve can sometimes produce an additional sound called a heart murmur.
A heart murmur is a sound—not a diagnosis.
VISUAL: Simplified heart with four valves highlighted and directional blood-flow arrows
Your Heart Has Its Own Electrical System
Your heart doesn't wait for you to tell it when to beat.
Specialized cells inside the heart generate and carry electrical signals that coordinate each heartbeat.
The signal normally begins in a small group of cells in the upper-right chamber called the sinoatrial—or SA—node.
Think of the SA node as your heart's natural pacemaker.
From Signal to Heartbeat
The electrical signal travels through the upper chambers, causing the atria to contract.
It then passes through another important area called the AV node, where the signal briefly slows before traveling into the ventricles.
That brief delay gives the upper chambers time to move blood into the lower chambers before the ventricles contract and pump blood forward.
Signal → Atria Contract → Brief Delay → Ventricles Contract → Repeat
Your heartbeat isn't random. It's an organized electrical event that creates a coordinated mechanical response.
So What Is Your Pulse?
Your heart rate is the number of times your heart beats per minute.
Your pulse is the pressure wave you can feel in an artery as the heart pumps blood forward.
They're closely related, but technically they describe two different things.
When the Electrical System Changes
If electrical signals are generated or conducted differently than normal, the heart may beat too fast, too slowly, or irregularly.
These abnormal heart rhythms are called arrhythmias.
VISUAL: Simplified heart highlighting SA Node → AV Node → ventricular electrical pathways
Your Blood Is Always on the Move
Now let's put everything together.
Your heart isn't simply pumping blood out. It's maintaining a continuous circuit between your heart, lungs, and body.
1. Body → Right Heart
After your body's tissues use oxygen, blood returns to the right side of the heart.
Body → Right Atrium → Right Ventricle
2. Right Heart → Lungs
The right ventricle pumps that blood to your lungs.
There, the blood releases carbon dioxide and picks up oxygen.
Right Ventricle → Lungs
3. Lungs → Left Heart
Oxygen-rich blood returns from the lungs to the left side of your heart.
Lungs → Left Atrium → Left Ventricle
4. Left Heart → Body
The left ventricle pumps that oxygen-rich blood through the aorta and out to the rest of your body.
Left Ventricle → Aorta → Body
And then the journey begins again.
Body → Right Heart → Lungs → Left Heart → Body
Arteries vs. Veins
Here's an important distinction:
Arteries carry blood AWAY from the heart.
Veins carry blood TOWARD the heart.
They're not named according to how much oxygen the blood carries.
That's why the pulmonary artery carries oxygen-poor blood from the heart to the lungs, while the pulmonary veins carry oxygen-rich blood back to the heart.
VISUAL: BODY → RIGHT HEART → LUNGS → LEFT HEART → BODY shown as one continuous loop
When You Understand the Heart, Heart Disease Makes More Sense
Your heart works because several systems are working together at the same time.
The heart muscle has to pump effectively.
The chambers have to fill and empty.
The valves have to keep blood moving forward.
The electrical system has to coordinate each heartbeat.
And the blood vessels have to deliver blood where your body needs it.
When something disrupts one part of that system, different heart problems can develop.
If blood flow to the heart muscle becomes blocked...
A heart attack can occur.
If the heart's electrical system isn't working normally...
An arrhythmia can develop.
If a valve becomes too narrow or doesn't close properly...
Blood flow through the heart can be disrupted.
If the heart becomes too weak or too stiff to meet the body's needs...
Heart failure can develop.
If the arteries supplying the heart become narrowed by plaque...
Coronary artery disease can develop.
Heart disease isn't one disease. It's a group of conditions that can affect different parts of the cardiovascular system in different ways.
Your Heart Is Working for You Every Day
Your heart doesn't need you to understand every piece of anatomy.
But understanding the basics can help you make sense of your blood pressure, pulse, cholesterol, symptoms, test results, medications, and conversations with your healthcare team.
You only have one heart.
Learning how it works is one step toward learning how to protect it.
Understand your heart. Know your risks. Pay attention to what your body is telling you.
Ready for the Next Step?
What Puts Your Heart at Risk?
Now that you understand how your heart works, learn about the factors that can increase your risk of heart disease—and which ones you can do something about.
BUTTON: Know Your Heart Disease Risk →
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Educational Disclaimer
This information is for general educational purposes and is not a substitute for individualized medical advice, diagnosis, or treatment. Talk with your healthcare professional about questions or concerns regarding your heart health. Seek appropriate medical attention for urgent or emergency symptoms.