Vein that carries oxygen poor blood to the heart from the lower part of the body

Your heart pumps blood throughout your body. A heart that works well is needed for good health. It can be helpful to learn more about how the heart works to understand the best way to treat it.

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Here’s a quick overview of the basic structure of a healthy heart.

Front view of the normal heart

The heart muscle

The heart muscle contracts and relaxes to pump blood to the lungs and the rest of the body. To do its work, the heart muscle needs a constant supply of oxygen. Oxygen is supplied to the heart muscle by the coronary arteries. These are the blood vessels that wrap around the surface of the heart.

• The left main coronary artery branches into the:
  • Circumflex coronary artery, which supplies blood to the back left side of the heart; and the
  • Left anterior descending coronary artery, which supplies blood to the front left side of the heart.
• The right coronary artery supplies blood to the bottom, right side and back of the heart muscle.

Inside the heart

Top view of a normal heart showing the coronary arteries and four valves

The inside of the heart is divided into right and left sides. Each side has an upper chamber called the atrium and a lower chamber called the ventricle. The two upper chambers (atria) receive blood from the lungs (left atrium) and body (right atrium). When these chambers contract, blood is pumped to the two lower chambers (left and right ventricles). As the lower chambers contract, blood is pumped to the lungs from the right ventricle and to the body from the left ventricle.

• Blood carries oxygen. The right side of the heart pumps oxygen-poor blood from the body to the lungs, where it receives oxygen. The left side of the heart pumps oxygen-rich blood from the lungs to the body. Once the body’s organs and tissues have removed the oxygen from the blood, the blood returns to the heart. The cycle is then repeated.
• Valves control the flow. There are four valves inside the heart. When the heart beats, valves act like one-way doors. This keeps blood moving forward through the heart and into the body and lungs.

Parts of the heart

The heart has four valves that open and close to allow blood to flow forward through the heart

• The superior vena cava carries oxygen-poor blood from the upper part of the body to the right atrium.
• The inferior vena cava carries oxygen-poor blood from the lower part of the body to the right atrium.
• The right atrium receives oxygen-poor blood from the body through the superior vena cava and the inferior vena cava.
• The tricuspid valve allows oxygen-poor blood to flow forward from the right atrium to the right ventricle.
• The right ventricle pumps oxygen-poor blood through the pulmonary valve.
• The pulmonary valve allows oxygen-poor blood to flow forward to the pulmonary artery.
• The pulmonary artery carries oxygen-poor blood to the lungs to receive oxygen.
• The pulmonary veins carry oxygen-rich blood from the lungs to the left atrium.
• The left atrium receives oxygen-rich blood from the lungs through the pulmonary veins.
• The mitral valve allows oxygen-rich blood to flow forward from the left atrium to the left ventricle.
• The left ventricle pumps oxygen-rich blood through the aortic valve.
• The aortic valve allows oxygen-rich blood to flow forward to the aorta.
• The aorta carries oxygen-rich blood to the rest of the body, except the lungs.
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• The circulatory system delivers oxygen and nutrients to cells and takes away wastes.
• The heart pumps oxygenated and deoxygenated blood on different sides.
• The types of blood vessels include arteries, capillaries and veins.

All cells in the body need to have oxygen and nutrients, and they need their wastes removed. These are the main roles of the circulatory system. The heart, blood and blood vessels work together to service the cells of the body. Using the network of arteries, veins and capillaries, blood carries carbon dioxide to the lungs (for exhalation) and picks up oxygen. From the small intestine, the blood gathers food nutrients and delivers them to every cell.
Blood consists of:

• Red blood cells – to carry oxygen
• White blood cells – that make up part of the immune system
• Platelets – needed for clotting
• Plasma – blood cells, nutrients and wastes float in this liquid.

The heart pumps blood around the body. It sits inside the chest, in front of the lungs and slightly to the left side. The heart is actually a double pump made up of four chambers, with the flow of blood going in one direction due to the presence of the heart valves. The contractions of the chambers make the sound of heartbeats.The right upper chamber (atrium) takes in deoxygenated blood that is loaded with carbon dioxide. The blood is squeezed down into the right lower chamber (ventricle) and taken by an artery to the lungs where the carbon dioxide is replaced with oxygen.The oxygenated blood travels back to the heart, this time entering the left upper chamber (atrium). It is pumped into the left lower chamber (ventricle) and then into the aorta (an artery). The blood starts its journey around the body once more.

Blood vessels

Blood vessels have a range of different sizes and structures, depending on their role in the body.

Arteries

Oxygenated blood is pumped from the heart along arteries, which are muscular. Arteries divide like tree branches until they are slender. The largest artery is the aorta, which connects to the heart and picks up oxygenated blood from the left ventricle. The only artery that picks up deoxygenated blood is the pulmonary artery, which runs between the heart and lungs.

Capillaries

The arteries eventually divide down into the smallest blood vessel, the capillary. Capillaries are so small that blood cells can only move through them one at a time. Oxygen and food nutrients pass from these capillaries to the cells. Capillaries are also connected to veins, so wastes from the cells can be transferred to the blood.

Veins

Veins have one-way valves instead of muscles, to stop blood from running back the wrong way. Generally, veins carry deoxygenated blood from the body to the heart, where it can be sent to the lungs. The exception is the network of pulmonary veins, which take oxygenated blood from the lungs to the heart.

Blood pressure

Blood pressure refers to the amount of pressure inside the circulatory system as the blood is pumped around.

Common problems

Some common problems of the circulatory system include:

• Aneurysm – a weak spot in the wall of an artery
• Atherosclerosis – a narrowing of the arteries caused by plaque deposits
• Heart disease – lack of blood supply to the heart because of narrowed arteries
• High blood pressure – can be caused by obesity (among other things)
• Varicose veins – problems with the valves that stop blood from running backwards.

Where to get help

• Your doctor
• In an emergency, always call triple zero (000)

Things to remember

• The circulatory system delivers oxygen and nutrients to cells and takes away wastes.
• The heart pumps oxygenated and deoxygenated blood on different sides.
• The types of blood vessels include arteries, capillaries and veins.

• Lloyd, M. & Gomez, J. 1981, The Complete Illustrated Medical Handbook, New Burlington Books, London.

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This page has been produced in consultation with and approved by:

This page has been produced in consultation with and approved by:

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