A journey to discover the "engine" of the organism: the heart. At the beginning of the episode Angela asks a series of questions: how many times does this organ beat in a lifetime? How does it work? What exactly happens when something goes wrong? The description of this "four-chamber pump" is careful and punctual, as in Piero Angela's style. When observed under a scanning electron microscope, the organ reveals many interesting details that are worth paying attention to.