In the field of medicine, what does the prefix- cardi- refer to?

Read the excerpt from "home front diary." jimmy simmons stopped by today to tell me that he had enlisted in the army. he asked me if i would write to him, and i said i would. i told him that i've been writing to my uncle arthur and susan's cousin john for about a year, and as an experienced correspondent i had some advice about all the censorship. "don't write down any information about your location or the number of soldiers in your unit because the censors will cut all of that away," i said. "in my experience, loose lips not only sink ships, they make letters look like snowflake decorations! ” well, he belly laughed over that one. how is the author's perspective different from jimmy's? the author has been to war and she can give jimmy advice. jimmy has become a soldier and does not believe the author’s advice. the author has experience writing to soldiers but jimmy does not. jimmy has more experience at letter writing than the author.