Teach Engineering offers standards-aligned STEM lesson plans that include assessments, worksheets, and engineering connections. The Heart of the Matter for elementary students covers heart basics and explores the way spaceflight influences the circulatory system. Put Your Heart Into Engineering for middle school students discusses heart valves and the value of prosthetic devices.
Texas Heart Institute's Project Heart has a terrific site for educators that is also linked to their site for kids. You'll find lesson plans for grades K-6 and ideas for interactive projects. Available in English and Spanish.
A Look at the Human Heart features lesson plans for hands-on investigations on topics such as heart anatomy, circulation, and measuring heartbeats. Scroll down to “Lesson Plans” and take a look.