How to listen to your heartbeat with a stethoscope

Every time the valves in your heart open and close to let blood flow through, it makes a 'dub-dub' sound. If you’ve ever wondered what your heart sounds like you can listen to your own heartbeat with a stethoscope made from rubber tubing, 2 funnels and a balloon. The typical stethoscopes that you see doctors using have a flat, round chest piece which is covered by a thin, tightly stretched piece of plastic called a diaphragm. When pressed against the chest it vibrates when a sound occurs and travels up the hollow tubing to the earpieces.

This stethoscope works on the same basis. The balloon stretched over the funnel becomes the diaphragm picking up the sounds and the smaller tunnel acting as the earpiece.

1 large funnel1 small funnel1 balloonLength of rubber tubing - you’ll need to make sure that your tubing can either fit inside or over the funnel spouts

Duct tape.

Insert the funnels either into each end of the rubber tubing and seal with your duct tape.

Blow the balloon up to stretch it out and then let the air out. Cut the end off the balloon and stretch it over the large funnel securing with your tape. Make sure your balloon is stretched as tight as possible and completely airtight so the vibrations from your heartbeat can travel through the tubing! Just a note here - we actually used a pair of rubber gloves and it worked, but the thinner balloon will pick up the vibrations of the heartbeat better. The stethoscope also has a better chance of working if you use the smaller funnel as the listening end and place the large funnel with the balloon in the centre of your chest, just over the heart.

If you’re struggling to hear your heartbeat, try moving the stethoscope slightly to the left and make sure the room is very quiet. You can also try running around or do some star jumps to get your heart going and listening to the increased heart rate!

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One of the most reassuring sounds a pregnant mother can hear is the steady thumping of her baby's heartbeat. Before 20 weeks of pregnancy, fetal heartbeats are typically monitored by doctors using a heart rate Doppler. While buying or renting an at-home Doppler is possible, it is often too expensive. Thankfully, after 20 weeks a baby's heartbeat can often be heard using a relatively cheap and easy-to-procure stethoscope.

Lie on your back in a quiet space. Background noise will make it more difficult to hear your baby's heartbeat.

Feel your stomach and try to locate your baby's back. This will feel like a smooth hard area. It is the best location to detect a fetal heartbeat.

Place the ear tips of the stethoscope in your ears and the chest piece along your baby's back.

Listen carefully for a few minutes. If you do not hear your baby's heartbeat, try moving the stethoscope up or down on your baby's back. Be aware that you may pick up your own heartbeat as well.

Don't worry if you do not hear your baby's heartbeat right away. How far along your pregnancy is, the baby's position, and the position of your placenta can all affect whether you detect your baby's heartbeat. If you are unsure whether you are hearing your baby's heartbeat or your own, try to time the beats-per-minute. The baby's heart rate will be much faster than your own--between 120 and 160 beats per minute.

If you have any questions or concerns about your baby's heartbeat, contact your doctor.

Bring Science Home

A Valentine's Day adventure from Science Buddies

Key concepts Stethoscope Health Exercise Amplification

The heart

Introduction
Around Valentine's Day heart-shaped images seem to be everywhere. But our actual hearts are at work all year—every hour, minute and second. The heart works hardest when we physically exert ourselves. How does its beating change? A doctor can figure this out by using a tool called a stethoscope, which is a long, thin plastic tube that has a small disc at one end and earpieces at the other. In this activity you will make a homemade stethoscope and use it to measure peoples' heart rates at rest and after exercising.

Background
You're probably familiar with how a stethoscope is used from visits to your own doctor. To listen to the heart, the doctor puts the stethoscope's flat disc or hollow cup on a patient's body and the earpieces go into the doctor's ears. But how does the stethoscope work? How does it allow the doctor to hear sounds inside of the patient's body?

The disc and the tube of the stethoscope amplify small sounds such as the sound of a patient's lungs, heart and other sounds inside the body, making them sound louder. The amplified sounds travel up the stethoscope's tube to the earpieces that the doctor listens through. Heartbeats can easily be heard using a good stethoscope. Every time a person's heart beats it contracts and acts as a powerful pump, which circulates blood that carries oxygen and nutrients throughout the body.

Materials • Duct tape or other strong tape • Scissors • Plastic funnel • A cardboard tube from a paper-towel roll • A volunteer who can safely exercise rigorously for one minute

• Stopwatch or clock that counts seconds

Preparation • Make sure you have a volunteer who can safely exercise rigorously for one minute. • Put the narrow end of the funnel into the cardboard tube. • Using a strip of duct tape or other strong tape, tape the funnel and cardboard tube together. Make sure there are no gaps or spaces where you tape them together.

• Your stethoscope is now ready to use! Practice listening to the heartbeat of a volunteer by putting the funnel on the left side of the volunteer's chest. Make sure the funnel is flat against their chest. Put your ear against the hole at the end of the cardboard tube. Do you hear a heartbeat?

• Before you begin the activity have your volunteer sit quietly in a chair for at least five minutes.

• Tip: If it's noisy or the volunteer is wearing thick clothing, it may be heard to hear the heartbeat, so you may need to adjust conditions accordingly.

Procedure • After the volunteer has been resting in a chair, listen to the heartbeat and count how many times it beats in 15 seconds.

• Multiply this number by four. This is the resting heart rate of the volunteer in beats per minute (bpm). What is the volunteer's resting heart rate?

• Ask the volunteer to exercise in place for one minute by doing jumping jacks or running in place. Right after the volunteer has stopped exercising, listen to the heartbeat and count how many times it beats in 10 seconds. Why do you think you do this for only 10 seconds instead of 15?
• Multiply this number by six. This is the heart rate right after exercising in bpm. What is the volunteer's heart rate now?
• How did the heart rate change after exercise? Why do you think it changed like it did?
• If a person regularly exercised, how do you think this would change his or her heart rate? How do you think that person's heart rate during rest and exercise would be different? Hint: Think about how regular exercise may change the heart.
• Extra: There are several different ways you can make a homemade stethoscope. For example, instead of a cardboard tube you could use a short piece of garden hose or plastic tubing. Or you could try varying the tube’s length. You could even try different size funnels. What homemade stethoscope design works best? What goes into making a good stethoscope design?
• Extra: In this activity you only tested one person's heart rate but you could try your stethoscope on several different people. How do different peoples' heart rates compare with one another? Do they all change a lot after exercising or do some change only a little bit or not at all? Does the heart rate correlate with a factor such as age, gender or body mass index (BMI)?
• Extra: A person should use at least 50 percent of their maximum heart rate when they are exercising for the activity to qualify as exercise. You can find out more about maximum and target heart rates and then apply this information to create an exercise routine. Based on this information, what physical activities does a given person do that qualifies as exercise?

Observations and results

Could you hear the volunteer's heartbeat using the homemade stethoscope? Did you find that when they exercised their heart rate increased compared with what their heart rate was when they were resting?

When people exercise, their bodies need more oxygen, and consequently their hearts beat faster and their heart rates increase. This is why you most likely found that when your volunteer exercised, their heart rate increased compared with their resting rate. In addition, genetics, gender, age and health all affect people's heart rates. The rates in people who exercise regularly usually will not increase as much during exercise and will return to a resting rate more quickly after exercise is stopped. Regular exercise strengthens the heart so that it does not need to work as hard.

Although you can determine someone's resting heart rate by counting the number of beats in 15 seconds and multiplying by four to get the bpm, to calculate a heart rate immediately after exercise, it is better to count the number of beats for 10 seconds and multiply that value by six (to get the bmp). Because the heart will quickly slow down after exercise ceases, its rate should be measured immediately after a person has stopped exercising (or while they exercise, if possible).

More to explore
Stethoscope , from KidsHealth
What is a stethoscope and how does a stethoscope work? , from Acoustic Heart
The evolution of an essential tool , from 3M Littmann Stethoscopes
Make Your Own Stethoscope , from Science Buddies

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