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3. Anatomy of the heart

Question: What is the heart?

Answer: The heart is a muscular pump but it is a very sophisticated one. It is made of muscle different from the sort that moves your arms and legs.

Heart muscle is particularly strong as it has to cope with the physical and emotional stresses of normal daily life and, of course, it never takes a rest (you hope!). It beats on average 100 000 times every 24 hours and pumps out between 5 and 20 litres of blood (1 litre equals just under 2 pints) every minute, depending on your body’s needs – more when you are being active than when you are resting. Every organ in the body needs oxygen to function normally and efficiently.

Fresh blood in the arteries delivers oxygen and energy to your body tissues and then, when it has given up its energy supply, blood carries away in the veins unwanted waste products including carbon dioxide.

The heart is the engine that pumps the blood around; normally it is the size of a clenched fist.

Question: Can you tell me what the coronary arteries are?

Answer: These are the tubes or vessels that supply your heart muscle with the oxygen and energy that it needs to pump efficiently. The vessels that carry the oxygen round the body are called arteries. Coronary arteries are tough tubes able to cope with the pressure pumped out by the heart. They are often confused with veins, such as those that we see on the back of the hand or on the legs (usually blue).

Veins bring used-up blood back to the heart. They are thinner than arteries and do not work or cope with high pressure in the same way as arteries do.

Think of your coronary arteries like the branches of a big tree with a main trunk branching out into smaller and smaller branches and twigs. There are three important coronary arteries with many branches. There is a left coronary artery which divides into two large branches, and a right coronary artery which is usually one big vessel. The coronary arteries arise from the main artery leaving your heart (the aorta), beginning just above the aortic valve. The most important coronary artery is the left main stem, which controls both branches of the left coronary artery and, as a result, most of the blood supply to your heart muscle.

The coronary arteries start at about 3-4 mm in size (like a thin straw) and as they feed the muscle they divide to reach all the layers of muscle. They run around the outside of the heart, sending their branches inwards.

The coronary arteries surround the heart muscle and send branches into the muscle, delivering blood containing oxygen. They start from the aorta just above the aortic valve. Dotted lines indicate the arteries running around the back of the heart.

Question: What happens when things go wrong with the coronary arteries?

Answer: The inner lining of your arteries is called the endothelium (pronounced ‘en-doe-thee-li-um’ which a smooth surface is allowing the blood to flow easily. If the endothelium becomes damaged, the tube becomes narrower, and the blood flow becomes turbulent with a chance of clots forming. Think of the artery as a roadway with a new road surface (the endothelium) – now imagine what happens to traffic flow if potholes are allowed to develop and road works cone off one or two lanes or humps are introduced – drive too fast and you will come a cropper! Your endothelium can become damaged by:


  • Cigarette smoking;
  • Poorly treated high blood pressure; and
  • A high level of cholesterol in your blood, causing localized deposits of fatty material (‘road humps’).


Narrowed coronary arteries can cause:


  • Angina;
  • Heart attack: the medical term for this is myocardial (heart muscle) infarction (death of part of the heart muscle);
  • Irregular heartbeats (some types of palpitations); and
  • Heart failure (where your muscle becomes weak).


Question: What is the aorta?

Answer: The aorta is the main artery leaving your heart. It sends blood to your head and then curves over to run down your chest along the spine. It passes along the back of your stomach, and at the top of the legs it divides into the big arteries which send branches down to your feet. Arteries branch off the aorta supplying arms, legs and all the important organs, such as the kidneys and liver.

Question: What are the valves?

Answer: The valves control the flow of blood into and out of your heart.

They open and shut just like a tap being turned on and off. When working normally, they act as one-way valves. The valves are on the inside of your heart, whereas the coronary arteries are on the outside.There are four valves – the aortic, mitral, pulmonary and tricuspid.

1. Blood returns to your heart through the veins. It has given up its oxygen to your brain, kidneys and muscle. It comes from the head region in a big vein called the superior (from the top of the body) vena cava, and from the lower body in a big vein called the inferior vena cava. It collects in a chamber called the right atrium.

2. The tricuspid valve separates this collecting chamber from the right ventricle, which is part of your muscle pump. (Ventricle is the medical word for pump.) You will notice the use of the word ‘right’ at this stage. This is because your heart is divided into two sides. The right side (on your right) collects used-up blood and passes it to your lungs to pick up oxygen, and the left collects oxygen-rich blood from the lungs and pumps it round the body. The muscle pump on the left is called the left ventricle. This is the most important part of the heart and the one that is most often damaged in a heart attack.

The circulation of blood from the body through the heart to the lungs. From the lungs the blood containing oxygen returns to the heart and circulates to the rest of the body. The atria are the collecting chambers; the ventricles are the muscle pump.

3. On the left side of your heart, blood leaving the lungs has been collecting in the left atrium. Blood therefore collects in the right atrium and left atrium at the same time. Separating the left atrium from the left ventricle is the mitral valve. The mitral valve opens at the same time as the tricuspid valve so that blood enters the right and left ventricles almost simultaneously.

4. Both the right ventricle and left ventricle contract at the same time. As the pressure builds up, the force closes the tricuspid and mitral valves (preventing any leaking backwards) and opens the pulmonary and aortic valves. Blood is ejected through the pulmonary valve to your lungs, and the aortic valve to your body. When the pump has emptied, the pressure drops, the pulmonary and aortic valves close, and the tricuspid and mitral valves open again; the cycle is then repeated.

Question: What keeps the right and left heart apart?

Answer: The muscle that divide your heart is called the septum. Between the right and left atrium, it is known as the atrial septum, and between the ventricles, the ventricular septum. When a hole occurs in your heart, we call it a defect. If it is between the atria (plural of atrium), it is known as an atrial septal defect (ASD) and if it is between the ventricles, it is a ventricular septal defect (VSD).



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