How Does Your Heart Work - Anatomy of the Heart, Coronary Arteries

Anatomy | Right Side | Left Side | Interior | Septum | Valves | Conduction | Blood Flow | Coronaries

How your heart works

Your heart is located under the ribcage in the center of your chest between your right and left lungs.A normal, healthy, adult heart is about the size of an average fist:

Heart Projection

Your heart is a muscle that pumps blood to the rest of your body. Your heart is part of your circulatory system, which consists of a network of arteries, veins, and capillaries that carry blood to and from all areas of your body. Electrical signals force your heart to contract and thus pump your blood to the rest of your body.

Your blood carries the oxygen and nutrients that your organs need to work normally. Blood also carries waste products such as carbon dioxide back to your heart and into your lungs to be passed out of your body and into the air. If disease or injury weakens your heart (your pump), your body's organs won't receive enough blood to work normally.

The heart has four chambers: The right and left atria and the right and left ventricles. The right side of your heart gets venous blood back from your body and then pumps it to your lungs. When you breathe in, oxygen passes from your lungs into your blood. Carbon dioxide, a waste product, is passed from the venous blood to your lungs and removed from your body when you breathe out.

The left atrium receives oxygen-rich blood from your lungs. The pumping action of your left ventricle sends this oxygen-rich blood to the rest of your body:

  1. Vena Cava
  2. Right Atrium
  3. Right Ventricle
  4. Main Pulmonary Artery
  5. Left & Right Pulmonary arteries
  6. Left & Right Pulmonary veins
  7. Left Atrium
  8. Left Ventricle
  9. Aorta
  10. Blood flow to the rest of your body

This animation shows how blood flows to and from your heart:

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The Right Side of Your Heart

The superior and inferior venae cavae are in blue to the left of the heart muscle as you look at the picture. These veins are the largest veins in your body. After your body's organs and tissues have used the oxygen in your blood, the venae cavae carry the venous (= oxygen-poor) blood back to the right atrium of your heart.

The superior vena cava carries venous blood from the upper parts of your body, including your head, chest, arms, and neck. The inferior vena cava carries venous blood from the lower parts of your body.

The blood from the venae cavae flows into your heart's right atrium and then on to the right ventricle. From the right ventricle, the blood is pumped through the pulmonary arteries to your lungs. There, the blood picks up more oxygen.

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The Left Side of Your Heart

The oxygen-rich (= arterial) blood passes from your lungs back to your heart, enters the left atrium and is pumped into the left ventricle. From there the arterial blood is pumped to the rest of your body through the aorta.

Like all of your organs, your heart needs blood rich with oxygen for its own energy supply.. This oxygen is supplied through the coronary arteries as blood is pumped out of your heart.

Your coronary arteries are initially located on your heart's surface. Deeper branches eventually reach the muscle cells where the energy exchange takes place. Procedures such as Percutaneous Cardiac Interventions (PCI) and Coronary Artery Bypass Grafting (CABG) are only performed to the arteries on the surface. Your coronary arteries (shown in red in the drawing) carry arterial blood to all parts of your heart.

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The Interior of Your Heart

Below is a picture of the inside of a heart:

Direction of heart blood flow

The blue arrow shows the direction in which venous (oxygen-poor) blood flows from the body to the lungs. The red arrow shows the direction in which arterial blood flows from the lungs to the rest of the body (from:

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Your Septum

The right and left sides of your heart are divided by an internal wall of tissue called the septum (see above).

Your Heart Valves

The picture shows your heart's four valves. Their function is to direct your venous (oxygen-poor) bloodflow forward to your lungs on the Right side from the right atrium to your lungs:

  • Tricuspid valve, between the Right atrium and Right ventricle
  • Pulmonary valve, between the Right ventricle and the Pulmonary artery

On the Left side oxygen rich blood from your lungs to your body:

  • Mitral valve, between the Left atrium and Left ventricle
  • Aortic valve, between the Left ventricle and aorta

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Nerve Conduction

Your heart's electrical system allow your heart to pump blood efficiently throughout your body. For each heart beat, the contraction of the heart muscle is initiated by electrical signals to the heart muscle.

Every single heart beat requires an electrical impulse to initiate it.The heart contains special tissue that produces and sends electrical impulses to the heart muscle. It is these impulses that trigger the heart to contract. Each time the heart beats, it sends out an electric-like signal. The heart's electrical signals can be measured with an EKG

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Your Blood Flow

Direction of heart blood flow

Once again, the arrows in the drawing show the direction that blood flows through your heart. The light blue arrows show that blood enters the right atrium of your heart from the superior and inferior venae cavae. From the right atrium, blood is pumped into the right ventricle.

From the right ventricle, blood is pumped to your lungs through the pulmonary arteries.The light red arrows show the arterial blood coming in from your lungs through the pulmonary veins into your heart's left atrium. From the left atrium, the blood is pumped into the left ventricle. The left ventricle pumps the blood to the rest of your body through the aorta.

For the heart to work properly, your blood must flow in only one direction. Your heart's valves make this possible. Both of your heart's ventricles have an inlet valve from the atria and an outlet valve leading to your arteries.

Healthy valves open and close in very exact coordination with the pumping action of your heart's atria and ventricles. Each valve has a set of flaps called leaflets or cusps that seal or open the valves. This allows pumped blood to pass through the chambers and into your arteries without backing up or flowing backward, just like a door closes a room.

(Adapted from National Heart Lung and Blood Institute,

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Your Coronary Arteries

The heart has 3 major coronary arteries. Two of these arteries arise from a common stem, called the left main coronary artery:

  • The left main coronary artery supplies the left side of the heart.
  • Its left anterior descending (LAD) branch supplies the front part of the heart.
  • The left circumflex (LCX) branch supplies the left lateral and back side of the heart.
  • Finally, the right coronary artery (RCA) is separate and supplies the right and the bottom parts of the heart.

Look at this animation of the coronary arteries:

Below is a picture of a normal human heart. Coronary arteries lay initially on the surface of the heart before they dive deep and eventually reach the muscle cells:

The illustration shows the front surface of a heart, including the coronary arteries and major blood vessels 

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