In this activity, each student represents a volume of blood passing through the circulatory system of that giant. Each student is provided with a red blood cell number (RBC #). This number is used to determine which circulation that particular erythrocyte visits on each trip through the body. Along the way, students pick up or leave cards that correspond to local functions. Each time the pacemaker (teacher) directs the heart to contract, a new group of students enters the system, and the preceding groups move to the next stop on their tour. Developed by Dr. Chuck Downey. Includes materials for 30 students, complete instructions, and an instructional video. Grades 9–AP.