After this activity, you'll have a deeper appreciation for the work your heart does, every minute of every day for your entire life.
The heart pumps out 2 oz. (1/4 cup) of blood per contraction. Cut some small paper/plastic cups down to hold 2 oz of water. (Dixie cups hold 3 oz. - fill one with 1/4 cup of water, mark the water line and cut).
Place two containers/tubs next to each other, on top of towels or newspapers. Fill one container 3/4 full of water.
(This would be a good candidate for an outside activity, but in my part of the world, February is not the time to go outside and play in the water, so just be prepared with newspapers, towels and maybe a mop, just in case).
Practice using the cut-down cup to transfer water from one container to the second. After you've practiced, return all the water to the original container.
When your partner/the teacher says to begin, use the cup to transfer water from one container to the second as quickly as you can. Count the number of cup-fulls you transfer. Your partner/the teacher will tell you to stop after one minute.
How many transfers did you make? Did you come close to 80? That's how many times your heart moved 2 oz. of blood during that minute.
Try again and try to go even faster this time. See if you can come close to matching your heart.