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An Experiment to Determine the Effect of Caffeine on Heart Rate

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Does the effect of an increasing volume of caffeine in an energy drink cause a corresponding increase in heart rate?


The heart rate should increase proportionately to the amount of caffeine present in the different amounts of the energy drink that is used. Caffeine is known to cause tachycardia, which is a disorder of the heart rate (pulse) because it beats too fast.


Variable Measured

Method of measuring/controlling variable

Independent variable

The volume of caffeine in the energy drink

25ml, 50ml, 75ml, 100ml and 125ml of Bison (energy drink) will be used for each experiment. The volume is measured using a measuring cylinder.

Dependent variable

The number of heart beats per minute of the person

This will be counted by a friend/family member by starting the stopwatch and counting the number of beats in a minute.

Controlled variables

The person taking the heart beat of the person doing the experiment

The same person will be used so that the experiment stays accurate. The same method is used while finding the heart rate.

The time gap between drinking the energy drink and taking the heart beat after drinking

This will remain as 1 hour for each experiment and a stopwatch will be used to ensure that the time gap remains 1 hour in each case.

The measuring cylinder used to measure the volume of the energy drink

The same 250ml measuring cylinder will be used while measuring the volume of the energy drink needed. Therefore the uncertainties will remain the same.

The temperature of the energy drink

The energy drink will remain in room temperature throughout the experiment and will be stored in the same room.


Apparatus –

Measuring cylinder


Bison energy drink (1880 ml)

Plastic cups (5)

Permanent marker

Using a measuring cylinder, pour 25ml, 50ml, 75ml, 100ml and 150ml of Bison into each of the plastic cups. Make sure they are all labeled using the permanent marker.

First get a friend/family member to find a pulse and count the heart beat in one minute. This can be done so by placing two fingers on the neck or placing two fingers on the opposite wrist. Record this data in a table.

Start off with the 25ml of Bison. Drink this volume of Bison and start the stopwatch.

After an hour, ask someone to measure the heart rate using the same methods stated above.

Once the data has been recorded, drink the next volume sample, which is 50ml and start the stopwatch. After an hour, measure the heart rate with the help of someone else.

Continue doing so until all volume samples have been drunk.

Repeat steps 1-6 five times over a course of five days. A total of 5-6 hours on each day will be dedicated towards this experiment. The data can be used to calculate an average, which makes the experiment more accurate.


Raw Data –

A table to show the heart rate after drinking a certain volume of an energy drink with a certain amount of caffeine.


Based on the results and graph, I can see that my hypothesis is proven correct; as the amount of caffeine increases, the heart rate also increase. However, the rate at which the heart rate increases is not extremely large as I can see from the graph that the line is not steep. The justification as to why the heart rate increases when the amount of caffeine increases is because large amounts of caffeine can cause tachycardia, which is a disorder of the heart rate (pulse) because it beats too fast. We can see from the data in the tables that when there is 5mg of caffeine present, the heart rate is about 74 beats/minute and when there is 30mg of caffeine present, the heart rate is about 90 beats/minute. I can see that there is a different between the results but it’s not very significant.

Limitations that were faced during this experiment included the measurement of the heart beat. In some cases, my friend/family member was unable to find my pulse when the time had come to record my heart rate. Therefore, there wasn’t enough accuracy in determining the heart rate. There were also cases where the heart rate was taken at a later time as I was unaware that the time limit had been reached. This also affected my results as the heart rate had more time to go back down to its normal pace. Such errors can only be avoided by being more accurate and careful.

The heart rate wasn’t exactly based on the amount of caffeine present in my body. For example, I found myself doing other activities that increased my heart rate, such as lifting heavy objects and going up and down the stairs. In some cases, I did this a few minutes before it was time to measure my heart rate, therefore getting an inaccurate set of results. This could have been avoided if I sat down in one place for an hour, making sure that my heart rate was only affected by the caffeine.

In order to get more reliable results, larger amounts of caffeine should have been used, therefore more energy drinks should have been drunk. This would give a larger variety of data, which would make it more interesting to interpret and conclude. For example, a total of 100mg of caffeine should have been used, which meant that a total of about 4600ml of energy drink would need to be drunk. This may not have been possible as drinking that much energy drink isn’t exactly good for a person’s health, but it would be interesting to see what the results would be.

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