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Key Concepts
Medicine, health, heart disease, circulatory system, cardiovascular system
A cup of red liquid with a spout attached releasing water into a baking dish, and a second cup filled with red liquid on the side


Why is it important to eat healthy and exercise? If you don’t, you might end up with a cardiovascular disease. These diseases are conditions that affect your heart and blood vessels. The job of your cardiovascular system is to transport blood through your heart, veins, and arteries, to provide oxygen and nutrients to your body. If this blood flow doesn’t work properly anymore, it can have serious consequences. In this activity, you will find out what happens to the blood flow of people that have a condition called coronary heart disease.

This activity is not appropriate for use as a science fair project. Good science fair projects have a stronger focus on controlling variables, taking accurate measurements, and analyzing data. To find a science fair project that is just right for you, browse our library of over 1,200 Science Fair Project Ideas or use the Topic Selection Wizard to get a personalized project recommendation.


To be healthy, every part of the human body needs to be supplied with oxygen and nutrients. The job of blood is to transport oxygen and nutrients by traveling through the body's circulatory system, also called the cardiovascular system (heart, veins, and arteries) and delivering them to the other parts of the body. The heart acts as a powerful pump that generates the force necessary to move the blood around the circulatory system. When something goes wrong with the body's circulatory system, it can lead to serious health consequences, including death.

The most common problem with the circulatory system is coronary heart disease, also called coronary artery disease. Coronary heart disease is caused by the buildup of cholesterol and other material, called plaque, in the arteries: the blood vessels that carry oxygenated blood from the heart to the organs. The heart disease that is caused by this buildup is known as atherosclerosis. Over time, as the plaque grows thicker, the arteries become narrower. As the arteries narrow, they cannot carry as much blood to the organs. The decrease in oxygenated blood can lead to chest pains and heart attacks. The plaque sometimes becomes dislodged and forms blood clots that block the blood flow, which can also cause heart attacks and strokes.

In this activity you will model what happens to blood flow when coronary heart disease narrows a person's arteries by comparing the blood flow through straws (arteries) of different diameters. Of course, you won’t use real blood, but colored water instead!


  • Plastic cups, 16 oz. (2)
  • Two straws with different diameters (a 2-inch piece of each)
  • Modeling clay
  • Stopwatch
  • Tray (big enough to fit 500 mL of water)
  • Water
  • Red food coloring
  • Measuring cup
  • Scissors
  • Permanent marker
  • Paper


  1. Add 400 mL of water and mark the water level on the outside of one of the 16 oz. plastic cups using a permanent marker. Then, make a mark on the other 16 oz. cup at the same height.
  2. Poke a hole into the sides of both cups, about one inch from the bottom. Widen the hole enough to comfortably fit each straw.
  3. Cut the straws to approximately 2-inch lengths. What do you think the straws represent in your blood flow model?
  4. Insert the straws into the holes. Make sure they are not squeezed. The straws should point down on the outside of the cup so water can flow out easily.
  5. Use modeling clay to seal the inside and outside of the hole around the straw.
  6. Prepare one liter of water. Add red food coloring to the water. What does the red water represent in your blood flow model?


  1. Start by placing the cup with the wide straw into the tray. What condition does the cup with the wide straw represent – a healthy or unhealthy cardiovascular system? Can you explain why?
  2. Then seal the end of the wider straw with a piece of modeling clay.
  3. Fill the cup up to the mark with red water. Improve the clay seal if needed.
  4. Remove the clay seal from the end of the straw and immediately start the stopwatch. Stop the stopwatch when the water stops flowing through the straw. How long does it take until the water stops flowing out of the cup? Record the time on a piece of paper.
  5. Place the cup with the narrow straw into the tray. What condition does the cup with the narrow straw represent? Why do you think this is the case?
  6. Seal the end of the narrow straw with a piece of modeling clay.
  7. Fill the cup with the narrow straw up to the mark with red water. Again, improve the clay seal if needed.
  8. Then remove the clay seal from the end of the straw and again start the stopwatch as soon as the water starts flowing. Stop the stopwatch when the water stops flowing. Record the time on a piece of paper. How long did it take this time until the water stopped flowing?
  9. Compare both times that you recorded on your paper. Which condition (wide or narrow straw) resulted in a faster and better blood flow? What does your result say about the blood flow in people with coronary heart disease (atherosclerosis)?

Extra: Calculate the flow rates of the ‘blood’ in both of your setups (wide and narrow straw) by dividing the water volume in mL at the beginning by the time it took for the water to flow out of the cup. How do both numbers compare?

Extra: Instead of using to different-sized straws, use two identical straws. Then use modeling clay to ‘clog’ on of the straws to actually model the plaque buildup inside an artery.

Observations and Results

You probably guessed right that the straws in your blood flow model represent the arteries in your body that transport blood from your heart to your organs. The red water in your model is the blood that flows through the arteries. Testing the setup with the wide straw simulates a healthy cardiovascular system in which the arteries are free from any plaque. As you should have noticed, the ‘blood flow’ out of the cup should have been relatively fast. The second setup with the narrow straw represents an unhealthy cardiovascular system. The artery (straw) is starting to get clogged with plaque and thus the diameter of the artery gets smaller and smaller. This also means that less blood can flow within the artery, which you should have observed in your experiment. With the narrower straw, the water takes much longer to flow out of the cup. In the worst case during coronary artery disease, the whole artery can get clogged and no blood can flow to your organs anymore. So, better eat healthy and exercise to keep your blood flowing!


Pour the red water into the sink. Dispose of the cups and the straws in the trash. You can dry your modeling clay and reuse it.

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Svenja Lohner, PhD, Science Buddies



Science Buddies |
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Key Concepts
Medicine, health, heart disease, circulatory system, cardiovascular system
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