All you need are scissors, a straw, and bottle tops from a soda or water bottle. Simple items you can find around your home.
Then we cut the straw vertically, so we could connect the straw to the top. After you're done, it should look like a sailboat.
Finding a very still surface is important, a variable that our friends noticed very quickly affected their experiment. Then we found where each child's pulse was on the inside of their elbow, and placed the tool there. While it takes a lot of focus and concentration, the children were excited when they noticed the tool waving along to the rhythm of a heartbeat. An experiment that is just as fun for adults as it is for children.