Doctors carry stethoscopes around their necks for many reasons: to look good, to get onto a ward if they have forgotten their ID badge, to remind themselves that they did at one point achieve a degree in medicine. The main reason, however, is to listen to people's hearts.

Your Heart

Your heart exists so you can get oxygen to parts of your body. It is in fact two pumps. One pumps the blood that's come back from the rest of the body to the lungs so it can load up on oxygen, and then back into the other pump. The second pump then pumps the blood that is now full of oxygen to the rest of your body so that it can use it.

Both the pumps are next to each other and both contract at the same time and work in the same way. They each consist of two chambers, one called an atrium¹ and one called a ventricle, separated by a simple valve that is controlled by pressure - if there is more pressure in the atrium than in the ventricle, the valve will be open; if there is more pressure in the ventricle, then the valve will be closed.

Step One, the Heart Fills up with Blood - Diastole

Blood flows into the atria from the rest of the body and from the lungs, pushes open the valves and fills the ventricles up.

Step Two, the Heart Contracts - Systole

The atria contract first pushing any blood in there into the ventricles, then very soon afterwards the ventricles contract. This increases the pressure in the ventricles so the valves close and the blood is pushed into the body and the lungs via the main arteries.

When the heart has stopped contracting and starts filling up again, there is less pressure in the ventricles than in the main blood vessels leading out from the heart. To stop the blood from flowing back into the ventricles, valves (at the beginning of the main blood vessels leading to the lungs and to the rest of the body) close.

The Heart Has Four Valves

When a doctor is listening to your heart they are listening to the sounds that the valves make when they shut, and they check that the blood is not making any sound flowing around the valves.

The two valves that separate that atria and ventricles are called the Mitral valve in the left atrium and the Tricuspid valve in the right one. The valves that stop blood flowing back into the heart are called the aortic valve² and the pulmonary valve³.

You Can Feel Your Heart

You can feel your heart beating by feeling your chest in the space beneath your fifth rib⁴, about as far as halfway along your collar bone. In medical jargon, you're feeling a beat in the 5th intercostal space in the mid-clavicular line. This is where the bottom tip of your heart, called the apex, is closest to the skin, and the beat you feel there is known as the apex beat.

You can usually only feel the left side of your heart as this is the side that is largest - it has to be large to pump blood around the whole body. If the right side of the heart is enlarged⁵ then it can sometimes be felt just to the left of the breastbone.

If you can feel the heart beating abnormally strongly through the chest, it is called a 'heave'.

Sounds Your Heart Makes

Two things can be ascertained from listening to the heart: firstly, whether the valves are opening and closing at the correct times, and secondly, whether there are opening and closing properly. You can't tell if the heart muscle is beating correctly or if the heart is pumping enough blood out.

The First Heart Sound

This is made by the Tricuspid and Mitral valves closing, at the the start of systole⁶. As the entire heart usually contracts at once, both heart valves usually close at once, making a single sound.

Sometimes the first heart sound is louder than usual. This could be because the person is thinner than normal or because the heart is working harder than normal⁷. It is also loud if one of the valves is stiffened so it isn't closing properly when contraction starts and is forced together by the contraction, this is known as Mitral stenosis.

Sometimes the first heart sound is softer than usual, which could be because one of the valves has become very stiffened and does not close at all. Alternately, it could be because there is fat between the heart and the stethoscope, or because there is fluid around the heart.

The Second Heart Sound

This is the sound of the aortic and pulmonary valves closing. When you take a deep breath in, the pressure inside your chest increases. This means that air is drawn into your lungs; it also means that venous blood (returning from the rest of the body) is drawn into the right ventricle faster than it normally would be. As there is more blood to get rid of in the right ventricle than the left, it takes a little longer to remove it. This means that the aortic valve will close before the pulmonary valve, so the second heart sound is heard as two sounds; this is known as a split sound. Usually the sounds are so close together that the two cannot be distinguished as separate sounds, though a spilt second heart sound is normal in children and young adults.

If the heart sound is split while breathing both in and out, this may be due to a defect in the wall between the two atria, commonly known as a hole in the heart. If it is spilt during breathing out but not during breathing in, then this is because the aortic valve is closing late due to the left side of the heart contracting later. This could be because the nerves supplying that part of the heart are damaged (known as left bundle branch block). When breathing in, the pulmonary valve is also closing later so it is not as noticeable.

If the second heart sound is split all the time, but the split sounds are slightly closer together during breathing in, then it could be due to right bundle branch block. This means that the nerves supplying the right side of the heart are damaged, so the pulmonary valve closes later than usual.

The second heart sound can be louder than normal if your blood pressure is high, because the left ventricle is working harder as it has a higher blood pressure to pump the blood against. If the aortic valve is hardened then it is softer because the valve isn't closing properly. It is also soft if the heart is failing, because a failing heart doesn't work as hard as a healthy one.

Abnormal Heart Sounds

The Third Heart Sound

This is the sound of blood rushing into the heart as soon as the Mitral and Tricuspid valves are open. It's usually heard just after the second heart sound. Some people say that it sounds like the 'tuc' in Kentucky. This is normal in children, and young or pregnant people. However in those over 40 it should be regarded as abnormal. It can be a sign of the heart being under stress, because too much fluid has gone into it, or of heart failure. It can be due to overload on the right side of the heart or the left side or both.

The Fourth Heart Sound

This is the sound of the atrium pumping blood into the ventricle just before it contracts, it is usually heard just before the first heart sound. Some people say that it sounds like the 'esse' in Tennessee. The presence of a fourth heart sound indicates that it is hard work for the atrium to pump blood into the ventricle, this means that the ventricle is abnormally stiff.

An Opening Snap

If the Mitral or Tricuspid valve is stiff then it can make a noise as it opens; this is known as an 'opening snap'.

Heart Murmurs

Heart sounds are the sound of the heart itself beating; heart murmurs are the sound of the blood flowing through the heart. They sound a lot like a 'whoosh'. Sometimes they're normal, and sometimes they're a sign of heart disease. Normal murmurs are usually at the start of systole, which is when the blood is pushed hardest, and usually they're quite soft.

Murmurs are described according to when and where they are heard, and how loud they are. They can be systolic or diastolic and are graded on a scale of 1 - 5 with 5 being the loudest. Very loud murmurs can be felt through the chest wall and are known as 'thrills'.

Ejection Systolic Murmurs are Often Caused by Aortic Stenosis

An 'ejection systolic murmur is heard in the the middle of systole. It is distinct from the initial first heart sound. This is because it's a problem with the aortic and pulmonary valves, and not with the Mitral and Tricuspid valves (which cause the first heart sound). It's caused by stenosis, ie, one of the valves is not opening properly.

Aortic stenosis causes a murmur that can also be heard in the clavicles and over the neck. This is because the aorta divides into blood vessels that run up the neck and under the clavicle. The murmur of aortic stenosis is heard best when the patient is sitting up and leaning forward because that brings the heart close to the chest wall. To distinguish it from a spilt second heart sound you need to ask the patient to take a deep breath and hold it.

Pan Systolic Murmurs are Often Caused by Mitral Regurgitation

These are heard as part of the first heart sound. This is because they are due to problems with the Mitral and Tricuspid valves that cause the first heart sound. The blood flows into the ventricles, then because the valve doesn't close it flows out again, causing a murmur.

In the UK, Mitral valve disease is very common because it is caused by high blood pressure, as the Mitral valve is under the most stress in the heart as it has to deal with the greatest pressure differences. It can also be damaged by a heart attack which has killed the papillary muscles, stopping it opening too far.

Murmurs Early in Diastole Can be Caused by Aortic Regurgitation

In aortic regurgitation, the blood goes out of the left ventricle, the aortic valve closes, causing the second heart sound, and then some blood leaks back through causing a murmur. Often aortic steonis and regurgitation occur on the same valve - this is known as mixed aortic valve disease.

A Murmur in the Middle of Diastole is Caused by Mitral Stenosis

During diastole the blood flows into the heart, through the open Mitral valve. If the Mitral valve is stiff, then blood makes a noise as it flows past it.

If there is an artificial heart valve, it makes a distinctive metal sound. Often this is so loud it can be heard without a stethoscope and is sometimes mistaken for the ticking of a clock.

If a doctor suspects that a valve is working abnormally then the next step will be to carry out an echocardiogram: an ultrasound scan of the heart identical to the one that pregnant women have⁸. This can show the exact movement of the valve and it can also show the amount of blood that the heart pumps out in each beat.