the "a" in cardi-a is from the latin and it just indicates that it's a noun, basically.
the suffixes you are more likely to need to know are things like the difference between "'osis," condition of (as in, diverticulosis, having diverticuli,) and -itis (as in diverticulitis, inflammation of the diverticuli). individual single letters are unlikely to be significant in that way.
adjectives, like tachy- or brady- or hyper- or hypo-, or epi- or endo-, describe the noun/root. they are most often before the root. but words in medical terminology come from many languages, and so those languages' rules influence how they are used today. for example, diabetes mellitus comes from the greek. ( μέλι (meli), honey.)
diabetes is named for one of its distressing symptoms. the disease was known to the greeks as diabts,
a word derived from the verb diabainein,
made up of the prefix dia-,
"across, apart," and the word bainein,
"to walk, stand." the verb diabeinein
meant "to stride, walk, or stand with legs asunder"; hence, its derivative diabts
meant "one that straddles," or specifically "a compass, siphon." the sense "siphon" gave rise to the use of diabts
as the name for a disease involving the discharge of excessive amounts of urine. diabetes
is first recorded in english, in the form diabete,
in a medical text written around 1425."
if it had been first described by a latin-speaking physician we would probably call it something like dulciurinosis, lol.