Despite student interest, the heart is often a poorly understood topic in biology. To help students understand this vital organ's physiology, the author created this investigation activity involving the mammalian heart and its role in the circulatory system. Students design, build, and demonstrate working artificial "hearts" to exhibit what they know about the circulatory system. This article describes how to incorporate the model heart activity into the classroom, including material that can be taught using the working product. (Contains 3 figures and 4 resources.)