Your heart is an amazing organ, pumping blood through your body and literally keeping you alive. However, building a realistic model of one — as explained in this write-up by Holiday McAllister — can actually be pretty simple.
Here, silicone is poured into a four-inch heart mold to create the structure, partially hollowed out to accommodate a metal gear micro servo.
This little motor rotates back and forth under control of an Arduino Uno, making it appear to pulse up and down on a table. One could see this enhanced in a variety of ways, perhaps with a bit of fake blood for an even more lifelike look, or with inputs to the Arduino for interactive capabilities.